Recording medium and information recording and reproducing method using the same

ABSTRACT

A recording medium comprises a substrate and a recording layer overlaid on the substrate. The recording layer comprises a material, which has properties such that, when recording light having a predetermined wavelength λ 1  is irradiated to the material, the material is capable of being caused to change into a fluorescent material and such that, when excitation light having a wavelength λ 2  is then irradiated to the thus formed fluorescent material, the fluorescent material is capable of being caused to produce fluorescence. The wavelength λ 1  of the recording light and the wavelength λ 2  of the excitation light may be identical or different. The substrate may be constituted of a material having properties such that, when the excitation light is irradiated to the material, the material does not produce fluorescence having a wavelength identical with the wavelength of the fluorescence produced by the fluorescent material.

BACKGROUND OF THE INVENTION

This is a divisional of application Ser. No. 09/793,721 filed Feb. 27,2001. The entire disclosure of the prior application, application Ser.No. 09/793,721 is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a recording medium. This inventionparticularly relates to a recording medium provided with a recordinglayer comprising a material, which has properties such that, when lighthaving a predetermined wavelength is irradiated to the material, thematerial is capable of being caused to change into a fluorescentmaterial. This invention also relates to a method and apparatus forrecording information, in which the recording medium is utilized. Thisinvention further relates to a method and apparatus for reproducinginformation, in which the recording medium is utilized.

DESCRIPTION OF THE RELATED ART

There have heretofore been proposed various recording media, each ofwhich is provided with a recording layer having properties such that,when light, such as a laser beam having been converged into a small beamdiameter, is irradiated to the recording layer, a change incharacteristics is caused to occur at a local area limited site of amaterial constituting the recording layer. By the utilization of theproperties of the recording layers of the recording media, information,such as image information or computer data, is capable of being recordedon the recording media. As the recording media described above,recording media, such as CD-R disks, wherein only one piece ofinformation is capable of being recorded at a single point on therecording layer, were popular in the past. Recently, recording mediaenabling multiple recording, wherein multiple pieces of information arecapable of being recorded at a single point on the recording layer andthe information is thus capable of being recorded at a high density,have been proposed.

As the recording media described above, recording media provided withrecording layers constituted of fluorescent materials have beenproposed. With the conventional recording media of the types describedabove, ordinarily, recording and reproduction of information areperformed by the utilization of the characteristics such that, whenrecording light is irradiated to the recording layer constituted of thefluorescent material and excitation light acting as reproducing light isthen irradiated to the site on the recording layer, which site has beenexposed to the recording light, the intensity of the fluorescence, whichis produced from the site having been exposed to the recording light,becomes lower than the intensity of the fluorescence, which is producedfrom the site having not been exposed to the recording light, or thewavelength of the fluorescence, which is produced from the site havingbeen exposed to the recording light, varies from the wavelength of thefluorescence, which is produced from the site having not been exposed tothe recording light.

However, with the conventional techniques for performing the recordingand the reproduction of the information in the manner described above,in cases where the excitation light is irradiated to the site having notbeen exposed to the recording light, as in cases where the excitationlight is irradiated to the site having been exposed to the recordinglight, the fluorescence is produced from the site having not beenexposed to the recording light, though the intensity or the wavelengthof the fluorescence varies from the intensity or the wavelength of thefluorescence produced from the site having been exposed to the recordinglight. Therefore, the problems occur in that the fluorescence producedfrom the site having not been exposed to the recording light acts as abackground, and a reproduced signal having a high signal-to-noise ratiocannot always be obtained.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a recordingmedium, wherein a reproduced signal having a high signal-to-noise ratiois capable of being obtained by the utilization of production offluorescence.

Another object of the present invention is to provide an informationrecording method, wherein information is capable of being recorded onthe recording medium.

A further object of the present invention is to provide an apparatus forcarrying out the information recording method.

A still further object of the present invention is to provide aninformation reproducing method, wherein a reproduced signal having ahigh signal-to-noise ratio is capable of being obtained from therecording medium.

Another object of the present invention is to provide an apparatus forcarrying out the information reproducing method.

A further object of the present invention is to provide a recordingmedium, wherein a reproduced signal having a high signal-to-noise ratiois capable of being obtained by the utilization of production offluorescence, and wherein multi-valued information is capable of beingrecorded at a recording unit, such as a single pit.

A still further object of the present invention is to provide amulti-valued information recording method, wherein multi-valuedinformation is capable of being recorded on the recording medium.

Another object of the present invention is to provide an apparatus forcarrying out the multi-valued information recording method.

A further object of the present invention is to provide a multi-valuedinformation reproducing method, wherein a reproduced signal having ahigh signal-to-noise ratio is capable of being obtained from therecording medium.

A still further object of the present invention is to provide anapparatus for carrying out the multi-valued information reproducingmethod.

Another object of the present invention is to provide a recordingmedium, wherein multiple recording is capable of being performed,wherein a reproduced signal having a high signal-to-noise ratio iscapable of being obtained, and wherein the recording medium is capableof being produced with a high producibility.

A further object of the present invention is to provide an informationrecording method, wherein multiple recording of information is capableof being performed at a high density on the recording medium.

A still further object of the present invention is to provide anapparatus for carrying out the information recording method for themultiple recording.

Another object of the present invention is to provide an informationreproducing method, wherein a reproduced signal having a highsignal-to-noise ratio is capable of being obtained from the recordingmedium, on which the multiple recording has been performed.

A further object of the present invention is to provide an apparatus forcarrying out the information reproducing method, wherein the reproducedsignal is capable of being obtained from the recording medium, on whichthe multiple recording has been performed.

The present invention provides a first recording medium, comprising:

i) a substrate, and

ii) a recording layer overlaid on the substrate,

wherein the recording layer comprises a material, which has propertiessuch that, when recording light having a predetermined wavelength λ1 isirradiated to the material, the material is capable of being caused tochange into a fluorescent material and such that, when excitation lighthaving a wavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence.

In the first recording medium in accordance with the present invention,the wavelength λ1 of the recording light and the wavelength λ2 of theexcitation light may be identical with each other. Alternatively, thewavelength λ1 of the recording light and the wavelength λ2 of theexcitation light may be different from each other.

Also, in the first recording medium in accordance with the presentinvention, the substrate should preferably be constituted of a materialother than materials, which have properties such that, when theexcitation light having the wavelength λ2 is irradiated to thematerials, the materials are caused to produce fluorescence having awavelength identical with the wavelength of the fluorescence produced bythe fluorescent material.

Further, the first recording medium in accordance with the presentinvention should preferably be modified such that the substratecomprises a dielectric material, a metal film is overlaid on one surfaceof the dielectric material, and the recording layer is overlaid on themetal film. In such cases, the metal film should preferably comprise ametal selected from the group consisting of gold and silver.

Furthermore, in the first recording medium in accordance with thepresent invention, the substrate should preferably comprise a materialpermeable to the excitation light having the wavelength λ2.

The present invention also provides a first information recordingmethod, in which information is recorded on the first recording mediumin accordance with the present invention, the method comprising the stepof:

irradiating the recording light having the predetermined wavelength λ1,which recording light carries recording information, to the recordinglayer of the recording medium, the material, which is located at a sitehaving been exposed to the recording light, being thereby caused tochange into the fluorescent material.

In the first information recording method in accordance with the presentinvention, an evanescent wave, which has been radiated out from a rangeof a diameter shorter than the wavelength of the recording light, shouldpreferably be employed as the recording light.

The present invention further provides a first information recordingapparatus, in which information is recorded on the first recordingmedium in accordance with the present invention, the apparatuscomprising:

recording means for irradiating the recording light having thepredetermined wavelength λ1, which recording light carries recordinginformation, to the recording layer of the recording medium in order tocause the material, which is located at a site having been exposed tothe recording light, to change into the fluorescent material.

The first information recording apparatus in accordance with the presentinvention should preferably be modified such that the recording means isprovided with a micro-aperture probe, which is provided with a lightpassage aperture having a diameter shorter than the wavelength of therecording light, the light passage aperture being formed at one end ofthe micro-aperture probe, and

the recording means irradiates an evanescent wave, which has beenradiated out from the light passage aperture of the micro-apertureprobe, to the recording layer.

Alternatively, the first information recording apparatus in accordancewith the present invention may preferably be modified such that therecording means irradiates an evanescent wave, which has been radiatedout from a solid immersion lens, to the recording layer.

The present invention still further provides a first informationreproducing method for reproducing recording information from the firstrecording medium in accordance with the present invention, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight carries the recording information, to the recording layer of therecording medium, the material, which is located at a site having beenexposed to the recording light, being thereby caused to change into thefluorescent material, the method comprising the steps of:

i) irradiating the excitation light having the wavelength λ2, whichfalls within an excitation wavelength region for the fluorescentmaterial, to the recording layer, the fluorescent material being therebycaused to produce the fluorescence, and

ii) detecting the fluorescence.

The first information reproducing method in accordance with the presentinvention may be modified such that light having the wavelength λ2identical with the wavelength λ1 of the recording light is employed asthe excitation light,

an intensity of the excitation light having the wavelength λ2 is set atan intensity lower than the intensity of the recording light, and

the excitation light having the thus set intensity is irradiated to therecording layer.

Alternatively, in the first information reproducing method in accordancewith the present invention, light having the wavelength λ2 differentfrom the wavelength λ1 of the recording light may be employed as theexcitation light.

Also, the first information reproducing method in accordance with thepresent invention should preferably be modified such that lightirradiated to a fine range is employed as the excitation light,

the recording layer is scanned with the excitation light, and

the fluorescence produced from the recording layer during the scanningwith the excitation light is detected with respect to each of positionswhich are being scanned.

In such cases, an evanescent wave, which has been radiated out from arange of a diameter shorter than the wavelength of the excitation light,should preferably be employed as the excitation light.

Further, the first information reproducing method in accordance with thepresent invention may be modified such that the excitation light isentered into the substrate so as to propagate through repeated totalreflection between two surfaces of the substrate,

an evanescent wave, which oozes out from the substrate toward therecording layer when the excitation light is thus entered into thesubstrate, is irradiated to the recording layer, and

the fluorescence, which has been produced from the recording layer whenthe evanescent wave is thus irradiated to the recording layer, isspatially resolved and detected.

Furthermore, in the first information reproducing method in accordancewith the present invention, in cases where the recording medium isconstituted such that the substrate comprises the dielectric material,the metal film is overlaid on one surface of the dielectric material,and the recording layer is overlaid on the metal film, the excitationlight should preferably be irradiated from the substrate side to therecording medium such that the excitation light impinges at a specificangle of incidence upon the metal film.

The present invention also provides a first information reproducingapparatus for reproducing recording information from the first recordingmedium in accordance with the present invention, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating the recording lighthaving the predetermined wavelength λ1, which recording light carriesthe recording information, to the recording layer of the recordingmedium, the material, which is located at a site having been exposed tothe recording light, being thereby caused to change into the fluorescentmaterial, the apparatus comprising:

i) excitation means for irradiating the excitation light having thewavelength λ2, which falls within an excitation wavelength region forthe fluorescent material, to the recording layer in order to cause thefluorescent material to produce the fluorescence, and

ii) read-out means for detecting the fluorescence.

The first information reproducing apparatus in accordance with thepresent invention should preferably be modified such that the excitationmeans employs light, which has the wavelength λ2 identical with thewavelength λ1 of the recording light, as the excitation light,

the excitation means sets an intensity of the excitation light havingthe wavelength λ2 at an intensity lower than the intensity of therecording light, and

the excitation means irradiates the excitation light having the thus setintensity to the recording layer.

Alternatively, the first information reproducing apparatus in accordancewith the present invention may be modified such that the excitationmeans irradiates light, which has the wavelength λ2 different from thewavelength λ1 of the recording light, as the excitation light to therecording layer.

Also, the first information reproducing apparatus in accordance with thepresent invention should preferably be modified such that the excitationmeans scans the recording layer with converged beam-like excitationlight, and the read-out means detects the fluorescence with respect toeach of positions which are being scanned with the excitation light.

Further, in the first information reproducing apparatus in accordancewith the present invention, in cases where the recording medium isconstituted such that the substrate comprises the dielectric material,the metal film is overlaid on one surface of the dielectric material,and the recording layer is overlaid on the metal film, the excitationmeans should preferably irradiate the excitation light to the recordingmedium such that the excitation light impinges upon the metal film fromthe substrate side.

Furthermore, the first information reproducing apparatus in accordancewith the present invention should preferably be modified such that theexcitation means scans the recording layer with an evanescent wave,which has been radiated out from a solid immersion lens, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.

Also, the first information reproducing apparatus in accordance with thepresent invention should preferably be modified such that the excitationmeans is provided with a micro-aperture probe, which is provided with alight passage aperture having a diameter shorter than the wavelength ofthe excitation light, the light passage aperture being formed at one endof the micro-aperture probe,

the excitation means scans the recording layer with an evanescent wave,which has been radiated out from the light passage aperture of themicro-aperture probe, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.

Further, the first information reproducing apparatus in accordance withthe present invention should preferably be modified such that theexcitation means irradiates the excitation light into the substrate suchthat the excitation light propagates through repeated total reflectionbetween two surfaces of the substrate, and such that an evanescent wave,which oozes out from the substrate toward the recording layer when theexcitation light is thus entered into the substrate, is irradiated tothe recording layer, and

the read-out means spatially resolves and detects the fluorescence,which has been produced from the recording layer when the evanescentwave is thus irradiated to the recording layer.

Furthermore, the first information reproducing apparatus in accordancewith the present invention should preferably be constituted such that anoptical system, through which the excitation light passes, contains onlyoptical members other than optical members, which have properties suchthat, when the excitation light having the wavelength λ2 is irradiatedto the optical members, the optical members are caused to producefluorescence having a wavelength identical with the wavelength of thefluorescence produced by the fluorescent material.

The present invention further provides a second recording medium,comprising:

i) a substrate, and

ii) a recording layer overlaid on the substrate,

wherein the recording layer comprises a material, which has propertiessuch that, when recording light having a predetermined wavelength λ1 isirradiated to the material, the material is capable of being caused tochange into a fluorescent material and such that, when excitation lighthaving a wavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence having an intensity in accordance with the intensity of therecording light.

In the second recording medium in accordance with the present invention,the wavelength λ1 of the recording light and the wavelength λ2 of theexcitation light may be identical with each other. Alternatively, thewavelength λ1 of the recording light and the wavelength λ2 of theexcitation light maybe different from each other.

Also, in the second recording medium in accordance with the presentinvention, the substrate should preferably be constituted of a materialother than materials, which have properties such that, when theexcitation light having the wavelength λ2 is irradiated to thematerials, the materials are caused to produce fluorescence having awavelength identical with the wavelength of the fluorescence produced bythe fluorescent material.

Further, the second recording medium in accordance with the presentinvention should preferably be modified such that the substratecomprises a dielectric material, a metal film is overlaid on one surfaceof the dielectric material, and the recording layer is overlaid on themetal film. In such cases, the metal film should preferably comprise ametal selected from the group consisting of gold and silver.

Furthermore, in the second recording medium in accordance with thepresent invention, the substrate should preferably comprise a materialpermeable to the excitation light having the wavelength λ2.

As a second information recording method, the present invention stillfurther provides a multi-valued information recording method, in whichmulti-valued information is recorded on the second recording medium inaccordance with the present invention, the method comprising the stepof:

irradiating the recording light having the predetermined wavelength λ1,which recording light has an intensity in accordance with themulti-valued information, to the recording layer of the recordingmedium, the material, which is located at a site having been exposed tothe recording light, being thereby caused to change into the fluorescentmaterial.

In the second multi-valued information recording method in accordancewith the present invention, an evanescent wave, which has been radiatedout from a range of a diameter shorter than the wavelength of therecording light, should preferably be employed as the recording light.

As a second information recording apparatus, the present invention alsoprovides a multi-valued information recording apparatus, in whichmulti-valued information is recorded on the second recording medium inaccordance with the present invention, the apparatus comprising:

recording means for irradiating the recording light having thepredetermined wavelength λ1, which recording light has an intensity inaccordance with the multi-valued information, to the recording layer ofthe recording medium in order to cause the material, which is located ata site having been exposed to the recording light, to change into thefluorescent material.

The second multi-valued information recording apparatus in accordancewith the present invention should preferably be modified such that therecording means is provided with a micro-aperture probe, which isprovided with a light passage aperture having a diameter shorter thanthe wavelength of the recording light, the light passage aperture beingformed at one end of the micro-aperture probe, and

the recording means irradiates an evanescent wave, which has beenradiated out from the light passage aperture of the micro-apertureprobe, to the recording layer.

Alternatively, the second multi-valued information recording apparatusin accordance with the present invention may preferably be modified suchthat the recording means irradiates an evanescent wave, which has beenradiated out from a solid immersion lens, to the recording layer.

As a second information reproducing method, the present inventionfurther provides a multi-valued information reproducing method forreproducing multi-valued information from the second recording medium inaccordance with the present invention, on which the multi-valuedinformation has been recorded, wherein the multi-valued information hasbeen recorded on the recording medium by irradiating the recording lighthaving the predetermined wavelength λ1, which recording light has anintensity in accordance with the multi-valued information, to therecording layer of the recording medium, the material, which is locatedat a site having been exposed to the recording light, being therebycaused to change into the fluorescent material, the method comprisingthe steps of:

i) irradiating the excitation light having the wavelength λ2, whichfalls within an excitation wavelength region for the fluorescentmaterial, to the recording layer, the fluorescent material being therebycaused to produce the fluorescence having an intensity in accordancewith the intensity of the recording light, and

ii) detecting the fluorescence.

The second multi-valued information reproducing method in accordancewith the present invention may be modified such that light having thewavelength λ2 identical with the wavelength λ1 of the recording light isemployed as the excitation light, an intensity of the excitation lighthaving the wavelength λ2 is set at an intensity lower than the intensityof the recording light, and

the excitation light having the thus set intensity is irradiated to therecording layer.

Alternatively, in the second multi-valued information reproducing methodin accordance with the present invention, light having the wavelength λ2different from the wavelength λ1 of the recording light may be employedas the excitation light.

Also, the second multi-valued information reproducing method inaccordance with the present invention should preferably be modified suchthat light irradiated to a fine range is employed as the excitationlight,

the recording layer is scanned with the excitation light, and

the fluorescence produced from the recording layer during the scanningwith the excitation light is detected with respect to each of positionswhich are being scanned.

In such cases, an evanescent wave, which has been radiated out from arange of a diameter shorter than the wavelength of the excitation light,should preferably be employed as the excitation light.

Further, the second multi-valued information reproducing method inaccordance with the present invention may be modified such that theexcitation light is entered into the substrate so as to propagatethrough repeated total reflection between two surfaces of the substrate,

an evanescent wave, which oozes out from the substrate toward therecording layer when the excitation light is thus entered into thesubstrate, is irradiated to the recording layer, and

the fluorescence, which has been produced from the recording layer whenthe evanescent wave is thus irradiated to the recording layer, isspatially resolved and detected.

Furthermore, in the second multi-valued information reproducing methodin accordance with the present invention, in cases where the recordingmedium is constituted such that the substrate comprises the dielectricmaterial, the metal film is overlaid on one surface of the dielectricmaterial, and the recording layer is overlaid on the metal film, theexcitation light should preferably be irradiated from the substrate sideto the recording medium such that the excitation light impinges at aspecific angle of incidence upon the metal film.

As a second information reproducing apparatus, the present inventionstill further provides a multi-valued information reproducing apparatusfor reproducing multi-valued information from the second recordingmedium in accordance with the present invention, on which themulti-valued information has been recorded, wherein the multi-valuedinformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight has an intensity in accordance with the multi-valued information,to the recording layer of the recording medium, the material, which islocated at a site having been exposed to the recording light, beingthereby caused to change into the fluorescent material, the apparatuscomprising:

i) excitation means for irradiating the excitation light having thewavelength λ2, which falls within an excitation wavelength region forthe fluorescent material, to the recording layer in order to cause thefluorescent material to produce the fluorescence having an intensity inaccordance with the intensity of the recording light, and

ii) read-out means for detecting the fluorescence.

The second multi-valued information reproducing apparatus in accordancewith the present invention should preferably be modified such that theexcitation means employs light, which has the wavelength λ2 identicalwith the wavelength λ1 of the recording light, as the excitation light,

the excitation means sets an intensity of the excitation light havingthe wavelength λ2 at an intensity lower than the intensity of therecording light, and

the excitation means irradiates the excitation light having the thus setintensity to the recording layer.

Alternatively, the second multi-valued information reproducing apparatusin accordance with the present invention may be modified such that theexcitation means irradiates light, which has the wavelength λ2 differentfrom the wavelength λ1 of the recording light, as the excitation lightto the recording layer.

Also, the second multi-valued information reproducing apparatus inaccordance with the present invention should preferably be modified suchthat the excitation means scans the recording layer with convergedbeam-like excitation light, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the excitation light.

Further, in the second multi-valued information reproducing apparatus inaccordance with the present invention, in cases where the recordingmedium is constituted such that the substrate comprises the dielectricmaterial, the metal film is overlaid on one surface of the dielectricmaterial, and the recording layer is overlaid on the metal film, theexcitation means should preferably irradiate the excitation light to therecording medium such that the excitation light impinges upon the metalfilm from the substrate side.

Furthermore, the second multi-valued information reproducing apparatusin accordance with the present invention should preferably be modifiedsuch that the excitation means scans the recording layer with anevanescent wave, which has been radiated out from a solid immersionlens, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.

Also, the second multi-valued information reproducing apparatus inaccordance with the present invention should preferably be modified suchthat the excitation means is provided with a micro-aperture probe, whichis provided with a light passage aperture having a diameter shorter thanthe wavelength of the excitation light, the light passage aperture beingformed at one end of the micro-aperture probe,

the excitation means scans the recording layer with an evanescent wave,which has been radiated out from the light passage aperture of themicro-aperture probe, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.

Further, the second multi-valued information reproducing apparatus inaccordance with the present invention should preferably be modified suchthat the excitation means irradiates the excitation light into thesubstrate such that the excitation light propagates through repeatedtotal reflection between two surfaces of the substrate, and such that anevanescent wave, which oozes out from the substrate toward the recordinglayer when the excitation light is thus entered into the substrate, isirradiated to the recording layer, and

the read-out means spatially resolves and detects the fluorescence,which has been produced from the recording layer when the evanescentwave is thus irradiated to the recording layer.

Furthermore, the second multi-valued information reproducing apparatusin accordance with the present invention should preferably beconstituted such that an optical system, through which the excitationlight passes, contains only optical members other than optical members,which have properties such that, when the excitation light having thewavelength λ2 is irradiated to the optical members, the optical membersare caused to produce fluorescence having a wavelength identical withthe wavelength of the fluorescence produced by the fluorescent material.

The present invention also provides a third recording medium,comprising:

i) a substrate, and

ii) a recording layer overlaid on the substrate,

wherein the recording layer comprises multiple kinds of materialsuniformly mixed together, each of which has properties such that, whenrecording light having a predetermined wavelength λ1 is irradiated tothe material, the material is capable of being caused to change into afluorescent material,

the multiple kinds of the materials are capable of being caused by therecording light having different wavelengths λ1 to change intofluorescent materials,

the fluorescent materials, which have been formed by the multiple kindsof the materials, are capable of being caused by excitation light havingdifferent wavelengths λ2 to produce fluorescence, and

the fluorescent materials, which have been formed by the multiple kindsof the materials, produce the fluorescence having different wavelengthsλ3.

The present invention further provides a fourth recording medium,comprising:

i) a substrate, and

ii) a recording layer overlaid on the substrate,

wherein the recording layer comprises multiple kinds of materialsuniformly mixed together, each of which has properties such that, whenrecording light having a predetermined wavelength λ1 is irradiated tothe material, the material is capable of being caused to change into afluorescent material,

the multiple kinds of the materials are capable of being caused by therecording light having different wavelengths λ1 to change intofluorescent materials,

the fluorescent materials, which have been formed by the multiple kindsof the materials, are capable of being caused by excitation light havingan identical wavelength λ2 to produce fluorescence, and

the fluorescent materials, which have been formed by the multiple kindsof the materials, produce the fluorescence having different wavelengthsλ3.

The present invention still further provides a fifth recording medium,comprising:

i) a substrate, and

ii) a recording layer overlaid on the substrate,

wherein the recording layer comprises multiple kinds of materialsuniformly mixed together, each of which has properties such that, whenrecording light having a predetermined wavelength λ1 is irradiated tothe material, the material is capable of being caused to change into afluorescent material,

the multiple kinds of the materials are capable of being caused by therecording light having different wavelengths λ1 to change intofluorescent materials,

the fluorescent materials, which have been formed by the multiple kindsof the materials, are capable of being caused by excitation light havingdifferent wavelengths λ2 to produce fluorescence, and

the fluorescent materials, which have been formed by the multiple kindsof the materials, produce the fluorescence having an identicalwavelength λ3.

In each of the third, fourth, and fifth recording media in accordancewith the present invention, by way of example, the recording layer maybe constituted of a thin film, which contains the multiple kinds of thematerials mixed together.

Also, each of the third, fourth, and fifth recording media in accordancewith the present invention should preferably be modified such that thesubstrate comprises a dielectric material a metal film is overlaid onone surface of the dielectric material, and the recording layer isoverlaid on the metal film. In such cases, the metal film shouldpreferably comprise a metal selected from the group consisting of goldand silver.

Further, in each of the third, fourth, and fifth recording media inaccordance with the present invention, the substrate should preferablycomprise a material permeable to the excitation light having thewavelengths λ2.

The present invention also provides a third information recordingmethod, in which information is recorded on the third, fourth, or fifthrecording medium in accordance with the present invention, the methodcomprising the step of:

irradiating beams of the recording light carrying recording informationand having a plurality of different wavelengths, each of whichwavelengths is capable of causing one of the multiple kinds of thematerials to change into the fluorescent material, to the recordinglayer of the recording medium, such that the beams of the recordinglight are capable of impinging upon an identical site on the recordinglayer, the multiple kinds of the materials, which are located at thesite having been exposed to the recording light, being thereby caused tochange into the fluorescent materials.

In the third information recording method in accordance with the presentinvention, an evanescent wave, which has been radiated out from a rangeof a diameter shorter than the wavelengths of the recording light,should preferably be employed as the recording light.

The present invention further provides an apparatus for carrying out thethird information recording method. Specifically, the present inventionfurther provides a third information recording apparatus, in whichinformation is recorded on the third, fourth, or fifth recording mediumin accordance with the present invention, the apparatus comprising:

recording means for irradiating beams of the recording light carryingrecording information and having a plurality of different wavelengths,each of which wavelengths is capable of causing one of the multiplekinds of the materials to change into the fluorescent material, to therecording layer of the recording medium, such that the beams of therecording light are capable of impinging upon an identical site on therecording layer, in order to cause the multiple kinds of the materials,which are located at the site having been exposed to the recordinglight, to change into the fluorescent materials.

The third information recording apparatus in accordance with the presentinvention should preferably be modified such that the recording means isprovided with a micro-aperture probe, which is provided with a lightpassage aperture having a diameter shorter than the wavelengths of therecording light, the light passage aperture being formed at one end ofthe micro-aperture probe, and

the recording means irradiates an evanescent wave, which has beenradiated out from the light passage aperture of the micro-apertureprobe, to the recording layer.

Alternatively, the third information recording apparatus in accordancewith the present invention may preferably be modified such that therecording means irradiates an evanescent wave, which has been radiatedout from a solid immersion lens, to the recording layer.

The present invention still further provides a third informationreproducing method for reproducing recording information from the thirdrecording medium in accordance with the present invention, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiatingbeams of the recording light carrying recording information and having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the method comprising the steps of:

i) irradiating the excitation light having a plurality of differentwavelengths, each of which wavelengths falls within an excitationwavelength region for one of the fluorescent materials, to the recordinglayer, the fluorescent materials being thereby caused to produce thefluorescence having different wavelengths, and

ii) detecting the fluorescence through wavelength discrimination.

The term “excitation light having a plurality of different wavelengths”does not necessarily mean that the excitation light having a certainwavelength and the excitation light having a different wavelength areemployed as independent excitation light. For example, the excitationlight may be one kind of white light of a wide wavelength region, whichranges over the excitation wavelength regions for the plurality of thefluorescent materials.

The present invention also provides a fourth information reproducingmethod for reproducing recording information from the fourth recordingmedium in accordance with the present invention, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating beams of therecording light carrying recording information and having a plurality ofdifferent wavelengths, each of which wavelengths is capable of causingone of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the method comprising the steps of:

i) irradiating one kind of the excitation light having a wavelength,which falls within an excitation wavelength region common to thefluorescent materials, to the recording layer, the fluorescent materialsbeing thereby caused to produce the fluorescence having differentwavelengths, and

ii) detecting the fluorescence through wavelength discrimination.

The present invention further provides a fifth information reproducingmethod for reproducing recording information from the fifth recordingmedium in accordance with the present invention, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating beams of therecording light carrying recording information and having a plurality ofdifferent wavelengths, each of which wavelengths is capable of causingone of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the method comprising the steps of:

i) irradiating the excitation light having a plurality of differentwavelengths, each of which wavelengths falls within an excitationwavelength region for one of the fluorescent materials, with differenttimings to the recording layer, the fluorescent materials being therebycaused to produce the fluorescence having the identical wavelength, and

ii) detecting the fluorescence.

The third, fourth, and fifth information reproducing methods inaccordance with the present invention may be modified such that lighthaving the wavelengths identical with the wavelengths of the recordinglight is employed as the excitation light,

an intensity of the excitation light having the wavelengths is set at anintensity lower than the intensity of the recording light, and

the excitation light having the thus set intensity is irradiated to therecording layer.

Alternatively, in the third, fourth, and fifth information reproducingmethods in accordance with the present invention, light having thewavelengths different from the wavelengths of the recording light may beemployed as the excitation light.

Also, the third, fourth, and fifth information reproducing methods inaccordance with the present invention should preferably be modified suchthat light irradiated to a fine range is employed as the excitationlight,

the recording layer is scanned with the excitation light, and thefluorescence produced from the recording layer during the scanning withthe excitation light is detected with respect to each of positions whichare being scanned.

In such cases, an evanescent wave, which has been radiated out from arange of a diameter shorter than the wavelength of the excitation light,should preferably be employed as the excitation light.

Further, the third, fourth, and fifth information reproducing methods inaccordance with the present invention may be modified such that theexcitation light is entered into the substrate so as to propagatethrough repeated total reflection between two surfaces of the substrate,

an evanescent wave, which oozes out from the substrate toward therecording layer when the excitation light is thus entered into thesubstrate, is irradiated to the recording layer, and

the fluorescence, which has been produced from the recording layer whenthe evanescent wave is thus irradiated to the recording layer, isspatially resolved and detected.

Furthermore, in the third, fourth, and fifth information reproducingmethods in accordance with the present invention, in cases where therecording medium is constituted such that the substrate comprises thedielectric material, the metal film is overlaid on one surface of thedielectric material, and the recording layer is overlaid on the metalfilm, the excitation light should preferably be irradiated from thesubstrate side to the recording medium such that the excitation lightimpinges at a specific angle of incidence upon the metal film.

The present invention still further provides a third informationreproducing apparatus for reproducing recording information from thethird recording medium in accordance with the present invention, onwhich the recording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiatingbeams of the recording light carrying recording information and having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the apparatus comprising:

i) excitation means for irradiating the excitation light having aplurality of different wavelengths, each of which wavelengths fallswithin an excitation wavelength region for one of the fluorescentmaterials, to the recording layer in order to cause the fluorescentmaterials to produce the fluorescence having different wavelengths, and

ii) read-out means for detecting the fluorescence through wavelengthdiscrimination.

The present invention also provides a fourth information reproducingapparatus for reproducing recording information from the fourthrecording medium in accordance with the present invention, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiatingbeams of the recording light carrying recording information and having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the apparatus comprising:

i) excitation means for irradiating one kind of the excitation lighthaving a wavelength, which falls within an excitation wavelength regioncommon to the fluorescent materials, to the recording layer in order tocause the fluorescent materials to produce the fluorescence havingdifferent wavelengths, and

ii) read-out means for detecting the fluorescence through wavelengthdiscrimination.

The present invention further provides a fifth information reproducingapparatus for reproducing recording information from the fifth recordingmedium in accordance with the present invention, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating beams of therecording light carrying recording information and having a plurality ofdifferent wavelengths, each of which wavelengths is capable of causingone of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the apparatus comprising:

i) excitation means for irradiating the excitation light having aplurality of different wavelengths, each of which wavelengths fallswithin an excitation wavelength region for one of the fluorescentmaterials, with different timings to the recording layer in order tocause the fluorescent materials to produce the fluorescence having theidentical wavelength, and

ii) read-out means for detecting the fluorescence.

The third, fourth, and fifth information reproducing apparatuses inaccordance with the present invention should preferably be modified suchthat the excitation means scans the recording layer with convergedbeam-like excitation light, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the excitation light.

Also, in the third, fourth, and fifth information reproducingapparatuses in accordance with the present invention, in cases where therecording medium is constituted such that the substrate comprises thedielectric material, the metal film is overlaid on one surface of thedielectric material, and the recording layer is overlaid on the metalfilm, the excitation means should preferably irradiate the excitationlight to the recording medium such that the excitation light impingesupon the metal film from the substrate side.

Further, the third, fourth, and fifth information reproducingapparatuses in accordance with the present invention should preferablybe modified such that the excitation means scans the recording layerwith an evanescent wave, which has been radiated out from a solidimmersion lens, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.

Furthermore, the third, fourth, and fifth information reproducingapparatuses in accordance with the present invention should preferablybe modified such that the excitation means is provided with amicro-aperture probe, which is provided with a light passage aperturehaving a diameter shorter than the wavelengths of the excitation light,the light passage aperture being formed at one end of the micro-apertureprobe,

the excitation means scans the recording layer with an evanescent wave,which has been radiated out from the light passage aperture of themicro-aperture probe, and

the read-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.

Also, the third, fourth, and fifth information reproducing apparatusesin accordance with the present invention should preferably be modifiedsuch that the excitation means irradiates the excitation light into thesubstrate such that the excitation light propagates through repeatedtotal reflection between two surfaces of the substrate, and such that anevanescent wave, which oozes out from the substrate toward the recordinglayer when the excitation light is thus entered into the substrate, isirradiated to the recording layer, and

the read-out means spatially resolves and detects the fluorescence,which has been produced from the recording layer when the evanescentwave is thus irradiated to the recording layer.

With the first recording medium in accordance with the presentinvention, the recording layer comprises the material, which has theproperties such that, when the recording light having the predeterminedwavelength λ1 is irradiated to the material, the material is capable ofbeing caused to change into the fluorescent material and such that, whenthe excitation light having the wavelength λ2 is then irradiated to thethus formed fluorescent material, the fluorescent material is capable ofbeing caused to produce the fluorescence. Therefore, with the firstinformation recording method in accordance with the present invention,the recording light having the predetermined wavelength λ1, whichrecording light carries the recording information, may be irradiated tothe recording layer of the recording medium, and the material, which islocated at a site having been exposed to the recording light, maythereby be caused to change into the fluorescent material. The site, atwhich the material has been caused to change into the fluorescentmaterial, may be utilized as, for example, one pit. In this manner,information, such as image information or computer data, is capable ofbeing recorded on the first recording medium in accordance with thepresent invention.

Also, with the first recording medium in accordance with the presentinvention, wherein the recording layer comprises the material having theproperties described above, in cases where the excitation light isirradiated to the recording layer when the recording information is tobe reproduced from the recording medium, basically, the fluorescence isnot produced from the site on the recording layer, which site has notbeen exposed to the recording light, and the fluorescence is producedfrom only the site on the recording layer, which site has been exposedto the recording light. Specifically, when the recording information isreproduced from the recording medium, the fluorescence, which will actas the background, is not produced from the site on the recordingmedium, which site has not been exposed to the recording light.Accordingly, a reproduced signal having a high signal-to-noise ratio iscapable of being obtained.

With the first recording medium in accordance with the presentinvention, the substrate for supporting the recording layer may beconstituted of the material other than materials, which have propertiessuch that, when the excitation light having the wavelength λ2 isirradiated to the materials, the materials are caused to producefluorescence having a wavelength identical with the wavelength of thefluorescence produced by the fluorescent material. In such cases, whenthe excitation light is irradiated to the recording layer in order forthe recording information to be reproduced from the recording medium,uniform fluorescence, which will act as the background, is not producedfrom the substrate. Therefore, a reproduced signal having asignal-to-noise ratio enhanced even further is capable of beingobtained.

Further, the first recording medium in accordance with the presentinvention has a simple constitution, wherein the material capable ofchanging into the fluorescent material when being exposed to the lightis over laid on the substrate. Therefore, the first recording medium inaccordance with the present invention is capable of being produced witha simple production process and with a high productivity.

With the first information recording method in accordance with thepresent invention, wherein the evanescent wave, which has been radiatedout from a range of a diameter shorter than the wavelength of therecording light, is employed as the recording light having thewavelength λ1, a pit having a size smaller than the light wavelength iscapable of being formed without being limited by the limit ofdiffraction. Therefore, the recording information is capable of beingrecorded at a high density.

In cases where the evanescent wave is to be utilized in the mannerdescribed above, the recording means constituted in the manner describedbelow may be utilized. Specifically, the recording means may be providedwith the micro-aperture probe, which is provided with the light passageaperture having a diameter shorter than the wavelength λ1 of therecording light, the light passage aperture being formed at one end ofthe micro-aperture probe, and the recording means may be constituted toirradiate the evanescent wave, which has been radiated out from thelight passage aperture of the micro-aperture probe, to the recordinglayer. Alternatively, the recording means may be constituted toirradiate the evanescent wave, which has been radiated out from thesolid immersion lens, to the recording layer.

With the first information reproducing method in accordance with thepresent invention, the excitation light having the wavelength λ2, whichfalls within the excitation wavelength region for the fluorescentmaterial and which is different from the wavelength λ1 of the recordinglight, may be irradiated to the recording layer, on which the recordinginformation has been recorded in the manner described above. In suchcases, the fluorescence is produced from the site on the recordinglayer, at which the material constituting the recording layer has beenchanged into the fluorescent material, and no fluorescence is producedfrom the site on the recording layer, at which the material constitutingthe recording layer has not been changed into the fluorescent material.Therefore, for example, in cases where the recording medium is scannedwith the excitation light, and the fluorescence produced from therecording medium is detected with respect to each of the positions whichare being scanned, the recording information is capable of being readout in accordance with the presence or absence of the fluorescence.

Also, with the first information reproducing method in accordance withthe present invention, the light having the wavelength λ2 identical withthe wavelength λ1 of the recording light may be employed as theexcitation light, and the intensity of the excitation light having thewavelength λ2 may be set at an intensity lower than the intensity of therecording light, such that the material constituting the recording layermay not be markedly caused by the excitation light to change into thefluorescent material. In such cases, the recording information iscapable of being read out appropriately.

Further, with the first information reproducing method in accordancewith the present invention, instead of the recording medium beingscanned with the excitation light, the excitation light may be enteredinto the substrate of the recording medium so as to propagate throughrepeated total reflection between the two surfaces of the substrate, andthe evanescent wave, which oozes out from the substrate toward therecording layer when the excitation light is thus entered into thesubstrate, may be irradiated to the recording layer. Also, thefluorescence, which has been produced from the recording layer when theevanescent wave is thus irradiated to the recording layer, may bespatially resolved and detected. In this manner, the recordinginformation is capable of being read out.

Furthermore, with the first information reproducing method in accordancewith the present invention, wherein the evanescent wave, which has beenradiated out from a range of a diameter shorter than the wavelength ofthe excitation light by use of the aforesaid micro-aperture probe, orthe like, is employed as the excitation light, the excitation light iscapable of being irradiated only to a range of a size smaller than thelight wavelength without being limited by the limit of diffraction.Therefore, the recording information, which has been recorded at the pitof the small size and at a high density, is capable of being reproducedaccurately.

With the first information reproducing method in accordance with thepresent invention, the recording information may be reproduced from therecording medium, which is constituted such that the substrate comprisesthe dielectric material, the metal film is overlaid on one surface ofthe dielectric material, and the recording layer is overlaid on themetal film. In such cases, the excitation light may be irradiated fromthe substrate side to the recording medium such that the excitationlight impinges at a specific angle of incidence upon the metal film. Asa result, surface plasmon resonance is excited at the metal film, and aplasma wave (a light wave) oozes out toward the recording layer.Therefore, the recording layer is capable of being excited by the plasmawave.

Also, with the first information reproducing method in accordance withthe present invention, the excitation light may be entered into thesubstrate of the recording medium so as to propagate through repeatedtotal reflection between the two surfaces of the substrate, and theevanescent wave, which oozes out from the substrate toward the recordinglayer when the excitation light is thus entered into the substrate, maybe irradiated to the recording layer. In such cases, the evanescent waveacting as the excitation light oozes out toward the recording layer overa wide range of the recording layer. Specifically, in such cases, theevanescent wave cannot be irradiated to only the range of the sizesmaller than the light wavelength. However, in such cases, thefluorescence, which has been produced from the recording layer when theevanescent wave is thus irradiated to the recording layer, may bespatially resolved and detected. In this manner, the fluorescence, whichis produced from the small pits described above, is capable of beingdetected with respect to each of the small pits.

Further, with the first information reproducing method in accordancewith the present invention, wherein the excitation light is entered intothe substrate of the recording medium in the manner described above, theexcitation light oozes out as the evanescent wave toward the recordinglayer. Therefore, the problems do not occur in that strong excitationlight enters into the means for detecting the fluorescence. Accordingly,in such cases, the problems do not occur in that the fluorescencedetecting means detects the excitation light, which constitutes muchnoise components. As a result, a reproduced signal having a highsignal-to-noise ratio is capable of being obtained.

With the second recording medium in accordance with the presentinvention, the recording layer comprises the material, which has theproperties such that, when the recording light having the predeterminedwavelength λ1 is irradiated to the material, the material is capable ofbeing caused to change into the fluorescent material and such that, whenthe excitation light having the wavelength λ2 is then irradiated to thethus formed fluorescent material, the fluorescent material is capable ofbeing caused to produce the fluorescence having an intensity inaccordance with the intensity of the recording light. Therefore, withthe second multi-valued information recording method in accordance withthe present invention, the recording light having the predeterminedwavelength λ1, which recording light carries the recording information,may be irradiated to the recording layer of the recording medium, andthe material, which is located at a site having been exposed to therecording light, may thereby be caused to change into the fluorescentmaterial. The site, at which the material has been caused to change intothe fluorescent material, may be utilized as, for example, one pit. Inthis manner, information, such as image information or computer data, iscapable of being recorded on the second recording medium in accordancewith the present invention.

Also, with the second recording medium in accordance with the presentinvention, when the excitation light is irradiated to the recordinglayer, the recording layer produces the fluorescence having an intensityin accordance with the intensity of the recording light. Therefore, incases where the intensity of the recording light is altered inaccordance with the multi-valued information, the multi-valuedinformation having been recorded on the recording layer is capable ofbeing reproduced in accordance with the detected intensity of thefluorescence.

Further, with the second recording medium in accordance with the presentinvention, wherein the recording layer comprises the material having theproperties described above, in cases where the excitation light isirradiated to the recording layer when the multi-valued information isto be reproduced from the recording medium, basically, the fluorescenceis not produced from the site on the recording layer, which site has notbeen exposed to the recording light, and the fluorescence is producedfrom only the site on the recording layer, which site has been exposedto the recording light. Specifically, when the multi-valued informationis reproduced from the recording medium, the fluorescence, which willact as the background, is not produced from the site on the recordingmedium, which site has not been exposed to the recording light.Accordingly, a reproduced signal having a high signal-to-noise ratio iscapable of being obtained.

With the second recording medium in accordance with the presentinvention, the substrate for supporting the recording layer may beconstituted of the material other than materials, which have propertiessuch that, when the excitation light having the wavelength λ2 isirradiated to the materials, the materials are caused to producefluorescence having a wavelength identical with the wavelength of thefluorescence produced by the fluorescent material. In such cases, whenthe excitation light is irradiated to the recording layer in order forthe multi-valued information to be reproduced from the recording medium,uniform fluorescence, which will act as the background, is not producedfrom the substrate. Therefore, a reproduced signal having asignal-to-noise ratio enhanced even further is capable of beingobtained.

Further, the second recording medium in accordance with the presentinvention has a simple constitution, wherein the material capable ofchanging into the fluorescent material when being exposed to the lightis overlaid on the substrate. Therefore, the second recording medium inaccordance with the present invention is capable of being produced witha simple production process and with a high productivity.

With the second multi-valued information recording method in accordancewith the present invention, wherein the evanescent wave, which has beenradiated out from a range of a diameter shorter than the wavelength ofthe recording light, is employed as the recording light having thewavelength λ1, a pit having a size smaller than the light wavelength iscapable of being formed without being limited by the limit ofdiffraction. Therefore, the multi-valued information is capable of beingrecorded at a high density.

In cases where the evanescent wave is to be utilized in the mannerdescribed above, the recording means constituted in the manner describedbelow may be utilized. Specifically, the recording means may be providedwith the micro-aperture probe, which is provided with the light passageaperture having a diameter shorter than the wavelength λ1 of therecording light, the light passage aperture being formed at one end ofthe micro-aperture probe, and the recording means may be constituted toirradiate the evanescent wave, which has been radiated out from thelight passage aperture of the micro-aperture probe, to the recordinglayer. Alternatively, the recording means may be constituted toirradiate the evanescent wave, which has been radiated out from thesolid immersion lens, to the recording layer.

With the second multi-valued information reproducing method inaccordance with the present invention, the excitation light having thewavelength λ2, which falls within the excitation wavelength region forthe fluorescent material and which is different from the wavelength λ1of the recording light, may be irradiated to the recording layer, onwhich the multi-valued information has been recorded in the mannerdescribed above. In such cases, the fluorescence is produced from thesite on the recording layer, at which the material constituting therecording layer has been changed into the fluorescent material, and nofluorescence is produced from the site on the recording layer, at whichthe material constituting the recording layer has not been changed intothe fluorescent material. Therefore, for example, in cases where therecording medium is scanned with the excitation light, and thefluorescence produced from the recording medium is detected with respectto each of the positions which are being scanned, the multi-valuedinformation is capable of being read out in accordance with the presenceor absence of the fluorescence.

Also, with the second multi-valued information reproducing method inaccordance with the present invention, the light having the wavelengthλ2 identical with the wavelength λ1 of the recording light may beemployed as the excitation light, and the intensity of the excitationlight having the wavelength λ2 may be set at an intensity lower than theintensity of the recording light, such that the material constitutingthe recording layer may not be markedly caused by the excitation lightto change into the fluorescent material. In such cases, the multi-valuedinformation is capable of being read out appropriately.

Further, with the second multi-valued information reproducing method inaccordance with the present invention, instead of the recording mediumbeing scanned with the excitation light, the excitation light may beentered into the substrate of the recording medium so as to propagatethrough repeated total reflection between the two surfaces of thesubstrate, and the evanescent wave, which oozes out from the substratetoward the recording layer when the excitation light is thus enteredinto the substrate, may be irradiated to the recording layer. Also, thefluorescence, which has been produced from the recording layer when theevanescent wave is thus irradiated to the recording layer, may bespatially resolved and detected. In this manner, the multi-valuedinformation is capable of being read out.

Furthermore, with the second multi-valued information reproducing methodin accordance with the present invention, wherein the evanescent wave,which has been radiated out from a range of a diameter shorter than thewavelength of the excitation light by use of the aforesaidmicro-aperture probe, or the like, is employed as the excitation light,the excitation light is capable of being irradiated only to a range of asize smaller than the light wavelength without being limited by thelimit of diffraction. Therefore, the multi-valued information, which hasbeen recorded at the pit of the small size and at a high density, iscapable of being reproduced accurately.

With the second multi-valued information reproducing method inaccordance with the present invention, the multi-valued information maybe reproduced from the recording medium, which is constituted such thatthe substrate comprises the dielectric material, the metal film isoverlaid on one surface of the dielectric material, and the recordinglayer is overlaid on the metal film. In such cases, the excitation lightmay be irradiated from the substrate side to the recording medium suchthat the excitation light impinges at a specific angle of incidence uponthe metal film. As a result, surface plasmon resonance is excited at themetal film, and a plasma wave (a light wave) oozes out toward therecording layer. Therefore, the recording layer is capable of beingexcited by the plasma wave.

Also, with the second multi-valued information reproducing method inaccordance with the present invention, the excitation light may beentered into the substrate of the recording medium so as to propagatethrough repeated total reflection between the two surfaces of thesubstrate, and the evanescent wave, which oozes out from the substratetoward the recording layer when the excitation light is thus enteredinto the substrate, may be irradiated to the recording layer. In suchcases, the evanescent wave acting as the excitation light oozes outtoward the recording layer over a wide range of the recording layer.Specifically, in such cases, the evanescent wave cannot be irradiated toonly the range of the size smaller than the light wavelength. However,in such cases, the fluorescence, which has been produced from therecording layer when the evanescent wave is thus irradiated to therecording layer, may be spatially resolved and detected. In this manner,the fluorescence, which is produced from the small pits described above,is capable of being detected with respect to each of the small pits.

Further, with the second multi-valued information reproducing method inaccordance with the present invention, wherein the excitation light isentered into the substrate of the recording medium in the mannerdescribed above, the excitation light oozes out as the evanescent wavetoward the recording layer. Therefore, the problems do not occur in thatstrong excitation light enters into the means for detecting thefluorescence. Accordingly, in such cases, the problems do not occur inthat the fluorescence detecting means detects the excitation light,which constitutes much noise components. As a result, a reproducedsignal having a high signal-to-noise ratio is capable of being obtained.

With each of the third, fourth, and fifth recording media in accordancewith the present invention, the recording layer comprises the materials,which have the properties such that, when the recording light having thepredetermined wavelengths is irradiated to the materials, the materialsare capable of being caused to change into the fluorescent materials.Therefore, with the third information recording method in accordancewith the present invention, the recording light carrying the recordinginformation may be irradiated to the recording layer of the recordingmedium, and the materials, which are located at a site having beenexposed to the recording light, may thereby be caused to change into thefluorescent materials. The site, at which the materials have been causedto change into the fluorescent materials, may be utilized as, forexample, one pit. In this manner, information, such as image informationor computer data, is capable of being recorded on each of the third,fourth, and fifth recording media in accordance with the presentinvention.

Also, with the third information recording method in accordance with thepresent invention, wherein the evanescent wave, which has been radiatedout from a range of a diameter shorter than the wavelengths of therecording light, is employed as the recording light, a pit having a sizesmaller than the light wavelengths is capable of being formed withoutbeing limited by the limit of diffraction. Therefore, the recordinginformation is capable of being recorded at a high density.

In cases where the evanescent wave is to be utilized in the mannerdescribed above, the recording means constituted in the manner describedbelow may be utilized. Specifically, the recording means may be providedwith the micro-aperture probe, which is provided with the light passageaperture having a diameter shorter than the wavelengths of the recordinglight, the light passage aperture being formed at one end of themicro-aperture probe, and the recording means may be constituted toirradiate the evanescent wave, which has been radiated out from thelight passage aperture of the micro-aperture probe, to the recordinglayer.

Further, with each of the third, fourth, and fifth recording media inaccordance with the present invention, the recording layer comprises themultiple kinds of the materials uniformly mixed together, whichmaterials are capable of being caused by the recording light havingdifferent wavelengths to change into the fluorescent materials.Therefore, with the third information recording method in accordancewith the present invention, beams of the recording light having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, may be irradiated to the recording layer of therecording medium, such that the beams of the recording light are capableof impinging upon an identical site on the recording layer. In thismanner, at the identical site on the recording layer, the multiple kindsof the materials are capable of being independently caused to changeinto the fluorescent materials, and the multiple recording is capable ofbeing thereby performed. With the third, fourth, and fifth recordingmedia in accordance with the present invention, which enables themultiple recording, the recording information is capable of beingrecorded at a high density.

Furthermore, each of the third, fourth, and fifth recording media inaccordance with the present invention has a simple constitution, whereinthe materials, such as compounds, are carried in the layer form on thesubstrate. Therefore, each of the third, fourth, and fifth recordingmedia in accordance with the present invention is capable of beingproduced with a simple production process and with a high productivity.

With each of the third, fourth, and fifth information reproducingmethods in accordance with the present invention, the excitation lighthaving the wavelengths, which fall within the excitation wavelengthregions for the fluorescent materials, may be irradiated to therecording layer, on which the recording information has been recorded inthe manner described above. In such cases, the fluorescence is producedfrom the site on the recording layer, at which the materialsconstituting the recording layer have been changed into the fluorescentmaterials, and no fluorescence is produced from the site on therecording layer, at which the materials constituting the recording layerhave not been changed into the fluorescent materials. Therefore, forexample, in cases where the recording medium is scanned with theexcitation light, and the fluorescence produced from the recordingmedium is detected with respect to each of the positions which are beingscanned, the recording information is capable of being read out inaccordance with the presence or absence of the fluorescence.

Also, with each of the third, fourth, and fifth information reproducingmethods in accordance with the present invention, instead of therecording medium being scanned with the excitation light, the excitationlight may be entered into the substrate of the recording medium so as topropagate through repeated total reflection between the two surfaces ofthe substrate, and the evanescent wave, which oozes out from thesubstrate toward the recording layer when the excitation light is thusentered into the substrate, may be irradiated to the recording layer.Also, the fluorescence, which has been produced from the recording layerwhen the evanescent wave is thus irradiated to the recording layer, maybe spatially resolved and detected. In this manner, the recordinginformation is capable of being read out.

With the third information reproducing method in accordance with thepresent invention, the excitation light having the plurality of thedifferent wavelengths, each of which wavelengths falls within theexcitation wavelength region for one of the fluorescent materials, isirradiated to the recording layer, the fluorescent materials beingthereby caused to produce the fluorescence having different wavelengths,and the fluorescence is detected through wavelength discrimination.Therefore, the recording information is capable of being read outindependently with respect to each of the multiple kinds of thematerials. In this manner, the information having been recorded with themultiple recording is capable of being reproduced accurately.

With the fourth information reproducing method in accordance with thepresent invention, one kind of the excitation light having thewavelength, which falls within the excitation wavelength region commonto the fluorescent materials, is irradiated to the recording layer, thefluorescent materials being thereby caused to produce the fluorescencehaving different wavelengths, and the fluorescence is detected throughwavelength discrimination. Therefore, the recording information iscapable of being read out independently with respect to each of themultiple kinds of the materials. In this manner, the information havingbeen recorded with the multiple recording is capable of being reproducedaccurately.

With the fifth information reproducing method in accordance with thepresent invention, the excitation light having the plurality of thedifferent wavelengths, each of which wavelengths falls within theexcitation wavelength region for one of the fluorescent materials, withdifferent timings to the recording layer, the fluorescent materialsbeing thereby caused to produce the fluorescence having the identicalwavelength, and the fluorescence is detected. Therefore, even if thefluorescence produced by the fluorescent materials has the identicalwavelength, the fluorescence is capable of being detected with differenttimings and independently with respect to each of the multiple kinds ofthe materials. Accordingly, the information having been recorded withthe multiple recording is capable of being reproduced accurately.

Further, with each of the third, fourth, and fifth informationreproducing methods in accordance with the present invention, whereinthe evanescent wave, which has been radiated out from a range of adiameter shorter than the wavelengths of the excitation light by use ofthe aforesaid micro-aperture probe, or the like, is employed as theexcitation light, the excitation light is capable of being irradiatedonly to a range of a size smaller than the light wavelengths withoutbeing limited by the limit of diffraction. Therefore, the recordinginformation, which has been recorded at the pit of the small size and ata high density, is capable of being reproduced accurately.

With each of the third, fourth, and fifth information reproducingmethods in accordance with the present invention, the recordinginformation may be reproduced from the recording medium, which isconstituted such that the substrate comprises the dielectric material,the metal film is overlaid on one surface of the dielectric material,and the recording layer is overlaid on the metal film. In such cases,the excitation light may be irradiated from the substrate side to therecording medium such that the excitation light impinges at a specificangle of incidence upon the metal film. As a result, surface plasmonresonance is excited at the metal film, and a plasma wave (a light wave)oozes out toward the recording layer. Therefore, the recording layer iscapable of being excited by the plasma wave.

Also, with each of the third, fourth, and fifth information reproducingmethods in accordance with the present invention, the excitation lightmay be entered into the substrate of the recording medium so as topropagate through repeated total reflection between the two surfaces ofthe substrate, and the evanescent wave, which oozes out from thesubstrate toward the recording layer when the excitation light is thusentered into the substrate, may be irradiated to the recording layer. Insuch cases, the evanescent wave acting as the excitation light oozes outtoward the recording layer over a wide range of the recording layer.Specifically, in such cases, the evanescent wave cannot be irradiated toonly the range of the size smaller than the light wavelength. However,in such cases, the fluorescence, which has been produced from therecording layer when the evanescent wave is thus irradiated to therecording layer, may be spatially resolved and detected. In this manner,the fluorescence, which is produced from the small pits described above,is capable of being detected with respect to each of the small pits.

Further, with each of the third, fourth, and fifth informationreproducing methods in accordance with the present invention, whereinthe excitation light is entered into the substrate of the recordingmedium in the manner described above, the excitation light oozes out asthe evanescent wave toward the recording layer. Therefore, the problemsdo not occur in that strong excitation light enters into the means fordetecting the fluorescence. Accordingly, in such cases, the problems donot occur in that the fluorescence detecting means detects theexcitation light, which constitutes much noise components. As a result,a reproduced signal having a high signal-to-noise ratio is capable ofbeing obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are schematic side views showing an embodiment ofthe recording medium in accordance with the present invention,

FIG. 2 is a side view showing a first embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 3 is a side view showing a second embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 4 is a side view showing a third embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 5 is a diagram showing a microscope photograph of a pit having beenformed on the recording medium with the information recording andreproducing apparatus of FIG. 4,

FIG. 6 is a side view showing a fourth embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 7 is a side view showing a fifth embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 8 is a side view showing a sixth embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 9 is a side view showing a seventh embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 10 is a side view showing an eighth embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 11 is a graph showing relationship between an intensity ofrecording light, which is irradiated to the recording medium inaccordance with the present invention, and an intensity of fluorescence,which is produced from the recording medium,

FIG. 12 is a graph showing an example of multi-valued information, whichhas been reproduced with the information recording and reproducingapparatus of FIG. 2,

FIG. 13 is a side view showing a ninth embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention,

FIG. 14 is a partially cutaway side view showing a major part of theinformation recording and reproducing apparatus of FIG. 13,

FIG. 15 is a side view showing a major part of a tenth embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention,

FIG. 16 is a side view showing a different embodiment of the recordingmedium in accordance with the present invention, and

FIG. 17 is a perspective view showing a further different embodiment ofthe recording medium in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinbelow be described in further detailwith reference to the accompanying drawings.

In the first, second, third, fourth, and fifth recording media inaccordance with the present invention, the recording layer comprises thematerial, which has the properties such that, when the recording lighthaving the predetermined wavelength λ1 is irradiated to the material,the material is capable of being caused to change into the fluorescentmaterial and such that, when the excitation light having the wavelengthλ2 is then irradiated to the material, the material is capable of beingcaused to produce the fluorescence. As the material constituting therecording layer of each of the first, second, third, fourth, and fifthrecording media in accordance with the present invention, the followingmay be employed appropriately: (1) A compound, which alone has theproperties described above. (2) A material, which comprises acombination of a plurality of compounds and which exhibits theproperties described above when the plurality of the compounds arecombined with one another.

By way of example, the compound, which alone has the propertiesdescribed above, may be a compound, in which a certain functional groupof a compound [FL] capable of producing the fluorescence has beenprotected with a protecting group [PR]-, and the production of thefluorescence is thereby restricted. The compound is represented byFormula (I) shown below. In the cases of the compound represented byFormula (I), the wavelength λ1 of the recording light causing thecompound to change into the fluorescent material, the wavelength λ2 ofthe excitation light, and the wavelength λ3 of the produced fluorescenceare different from one another.[FL]−[PR]  (I)wherein [FL] represents the compound residue capable of producing thefluorescence, and [PR] represents the group capable of being separatedfrom [FL] when light is irradiated to [FL].

Examples of the compounds represented by Formula (I) include thefollowing:

By way of example, the material, which comprises a combination of aplurality of compounds and which exhibits the properties described abovewhen the plurality of the compounds are combined with one another, maybe a material, which comprises a combination of a chemical species [FL]capable of producing the fluorescence and a chemical species [Q] capableof quenching the fluorescence. The material is represented by Formula(II) shown below. In the cases of the compound represented by Formula(II), the wavelength λ1 of the recording light causing the compound tochange into the fluorescent material and the wavelength λ2 of theexcitation light are identical with each other and different from thewavelength λ3 of the produced fluorescence.[FL]+[Q]  (II)wherein [FL] represents the chemical species capable of producing thefluorescence, and [Q] represents the chemical species capable ofquenching the fluorescence.

The chemical species [FL] in the compound represented by Formula (II)should preferably be the compound represented by Formula (II-1) shownbelow. The chemical species [Q] in the compound represented by Formula(II) should preferably be the compound represented by Formula (II-2)shown later.

wherein Z¹ and Z² each represent an atom group necessary for forming afive-membered or six-membered, nitrogen-containing heterocyclic ring;R³⁰ and R³¹ each independently represent an alkyl group or an arylgroup; L³, L⁴, L⁵, L⁶, and L⁷ each independently represent a substitutedor unsubstituted methine group, provided that, in cases where L³ to L⁷are substituted by substituents, the substituents may be connected withone another to form a ring; p and q each independently represent 0 or 1;n1 and n2 each independently represent 0, 1, or2; M1 represents a chargebalancing counter ion; and m1 represents a number necessary for keepingcharge balance.

The symmetric or asymmetric cyanine dye represented by Formula (II-1)will be described hereinbelow. Examples of the nucleuses formed with Z¹and Z² in Formula (II-1) include a 3,3-dialkylindolenine nucleus, a3,3-dialkylbenzoindolenine nucleus, a thiazole nucleus, a benzothiazolenucleus, a naphthothiazole nucleus, a thiazoline nucleus, an oxazolenucleus, a benzoxazole nucleus, a naphthoxazole nucleus, an oxazolinenucleus, a selenazole nucleus, a benzoselenazole nucleus, anaphthoselenazole nucleus, a selenazoline nucleus, a tellurazolenucleus, a benzotellurazole nucleus, a naphthotellurazole nucleus, atellurazoline nucleus, an imidazole nucleus, a benzoimidazole nucleus, anaphthoimidazole nucleus, a pyridine nucleus, a quinoline nucleus, anisoquinoline nucleus, an imidazo [4,5-b] quinoxaline nucleus, anoxadiazole nucleus, a thiadiazole nucleus, a tetrazole nucleus, and apyrimidine nucleus.

If possible, the five-membered or six-membered nitrogen-containingheterocyclic rings enumerated above may have a substituent. Examples ofthe substituents include those exemplified later as the substituents R¹,R², and R³ described with respect to Formula (II-2), which will be shownlater.

Specifically, examples of the substituents include a halogen atom or asubstituent formed by combining a carbon atom, an oxygen atom, anitrogen atom and a sulfur atom, and specifically, an alkyl group, analkenyl group, an aralkyl group, an aryl group, a heterocyclic group, ahalogen atom, a cyano group, a nitro group, a mercapto group, a hydroxylgroup, an alkoxy group, an aryloxy group, an alkylthio group, anarylthio group, an acyloxy group, an amino group, an alkylamino group,an amido group, a sulfoneamido group, a sulfamoylamino group, analkoxycarbonylamino group, an alkoxysulfonylamino group, an ureidogroup, a thioureido group, an acyl group, an alkoxycarbonyl group, acarbamoyl group, an alkylsulfonyl or arylsulfonyl group, analkylsulfinyl group, a sulfamoyl group, a carboxyl group (including asalt), and a sulfo group (including a salt). The above-enumeratedsubstituents may further be substituted with the substituents.

Examples of the substituents will hereinbelow be described in moredetail.

The alkyl group may be a straight-chain, branched, or cyclic alkyl grouphaving 1 to 18 carbon atoms (preferably 1 to 8 carbon atoms), whichgroup may optionally have a substituent. Examples of the alkyl groupsinclude methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl,2-hydroxyethyl, 4-carboxybutyl, hexyl, octyl, benzyl, and phenethyl.

The alkenyl group may be a straight-chain, branched, or cyclic alkenylgroup having 2 to 18 carbon atoms (preferably 2 to 8 carbon atoms).Examples of the alkenyl groups include vinyl, allyl, 1-propenyl,2-pentenyl, 1,3-butadienyl, and 2-octenyl.

The aralkyl group may be an aralkyl group having 7 to 10 carbon atomsand may be, for example, benzyl.

The aryl group may be an aryl group having 6 to 10 carbon atoms, whichgroup may optionally have a substituent. Examples of the aryl groupsinclude phenyl, naphthyl, 4-carboxyphenyl, 3-carboxyphenyl,3,5-dicarboxyphenyl, 4-methanesulfonamidophenyl, and4-butanesulfonamidophenyl.

The heterocyclic group may be a five-membered or six-membered, saturatedor unsaturated heterocyclic group comprising a carbon atom, a nitrogenatom, an oxygen atom, or a sulfur atom, in which the number of thehetero atom and the kind of the element constituting the ring may be atleast one. Examples of the heterocyclic groups include an oxazole ring,a benzoxazole ring, a 5-carboxybenzoxazole ring, a thiazole ring, animidazole ring, a pyridine ring, a sulfolane ring, a furan ring, athiophene ring, a pyrazole ring, a pyrrole ring, a chroman ring, and acoumarin ring.

Examples of the halogen atoms include a fluorine atom, a chlorine atom,and a bromine atom.

The alkoxy group may be an alkoxy group having 1 to 18 carbon atoms(preferably 1 to 8 carbon atoms). Examples of the alkoxy groups includemethoxy, ethoxy, propoxy, and butoxy.

The aryloxy group may be an aryloxy group having 6 to 10 carbon atoms,which group may optionally have a substituent. Examples of the aryloxygroups include phenoxy and p-methoxyphenoxy.

The alkylthio group may be an alkylthio group having 1 to 18 carbonatoms (preferably 1 to 8 carbon atoms) Examples of the alkylthio groupsinclude methylthio and ethylthio.

The arylthio group may be an arylthio group having 6 to 10 carbon atomsand may be, for example, phenylthio.

The acyloxy group may be an acyloxy group having 1 to 18 carbon atoms(preferably 1 to 8 carbon atoms) Examples of the acyloxy groups includeacetoxy, propanoyloxy, pentanoyloxy, and octanoyloxy.

The alkylamino group may be an alkylamino group having 1 to 18 carbonatoms (preferably 1 to 8 carbon atoms) Examples of the alkylamino groupsinclude methylamino, dimethylamino, diethylamino, dibutylamino, andoctylamino.

The amido group may be an amido group having 1 to 18 carbon atoms(preferably 1 to 8 carbon atoms). Examples of the amido groups includeacetamido, propanoylamino, pentanoylamino, octanoylamino,octanoylmethylamino, and benzamido.

The sulfonamido group may be a sulfonamido group having 1 to 18 carbonatoms (preferably 1 to 8 carbon atoms). Examples of the sulfonamidogroup include methanesulfonamido, ethanesulfonamido, propylsulfonamido,butanesulfonamido, and benzenesulfonamido.

The alkoxycarbonylamino group may be an alkoxycarbonylamino group having1 to 18 carbon atoms (preferably 1 to 8 carbon atoms). Examples of thealkoxycarbonylamino groups include methoxycarbonylamino andethoxycarbonylamino.

The alkoxysulfonylamino group may be an alkoxysulfonylamino group having1 to 18 carbon atoms (preferably 1 to 8 carbon atoms) Examples of thealkoxysulfonylamino groups include methoxysulfonylamino andethoxysulfonylamino.

The sulfamoylamino group may be a sulfamoylamino group having 0 to 18carbon atoms (preferably 0 to 8 carbon atoms), which group mayoptionally have a substituent. Examples of the sulfamoylamino groupsinclude methylsulfamoylamino, dimethylsulfamoylamino,ethylsulfamoylamino, propylsulfamoylamino, and octylsulfamoylamino.

The ureido group may be a ureido group having 1 to 18 carbon atoms(preferably 1 to 8 carbon atoms), which group may optionally have asubstituent. Examples of the ureido groups include ureido, methylureido,N,N-dimethylureido, and octylureido.

The thioureido group may be a thioureido group having 1 to 18 carbonatoms (preferably 1 to 8 carbon atoms), which group may optionally havea substituent. Examples of the thioureido groups include thioureido,methylthioureido, N,N-dimethylthioureido, and octylthioureido.

The acyl group may be an acyl group having 1 to 18 carbon atoms(preferably 1 to 8 carbon atoms). Examples of the acyl groups includeacetyl, benzoyl, and propanoyl.

The alkoxycarbonyl group maybe an alkoxycarbonyl group having 1 to 18carbon atoms (preferably 1 to 8 carbon atoms). Examples of thealkoxycarbonyl groups include methoxycarbonyl, ethoxycarbonyl, andoctyloxycarbonyl.

The carbamoyl group may be a carbamoyl group having 1 to 18 carbon atoms(preferably 1 to 8 carbon atoms), which group may optionally have asubstituent. Examples of the carbamoyl groups include carbamoyl,N,N-dimethylcarbamoyl, and N-ethylcarbamoyl.

The alkylsulfonyl or arylsulfonyl group may be an alkylsulfonyl orarylsulfonyl group having 1 to 18 carbon atoms (preferably 1 to 8 carbonatoms). Examples of the alkylsulfonyl or arylsulfonyl groups includemethanesulfonyl, ethanesulfonyl, and benzenesulfonyl.

The alkylsulfinyl group may be an alkylsulfinyl group having 1 to 18carbon atoms (preferably 1 to 8 carbon atoms). Examples of thealkylsulfinyl groups include methanesulfinyl, ethanesulfinyl, andoctanesulfinyl.

The sulfamoyl group may be a sulfamoyl group having 0 to 18 carbon atoms(preferably 0 to 8 carbon atoms), which group may optionally have asubstituent. Examples of the sulfamoyl groups include sulfamoyl,dimethylsulfamoyl, ethylsulfamoyl, butylsulfamoyl, octylsulfamoyl, andphenylsulfamoyl.

In particular, Z¹ and Z² should preferably each represent a substitutedor unsubstituted 3,3-dialkylindolenine nucleus, or a substituted orunsubstituted 3,3-dialkylbenzoindolenine nucleus.

Also, R³⁰ and R³¹ should preferably each independently represent analkyl group.

The alkyl group represented by each of R³⁰ and R³¹ may be a substitutedor unsubstituted, straight-chain, branched, or cyclic alkyl group having1 to 18 carbon atoms (preferably 1 to 8 carbon atoms). Examples of thesubstituents for the alkyl group include those exemplified above as thesubstituents for the nitrogen-containing heterocyclic ring, andpreferable substituents for the alkyl group are the same as thosedescribed above with respect to the substituents for thenitrogen-containing heterocyclic ring. The alkyl group should preferablybe an unsubstituted alkyl group or an alkyl group substituted by an arylgroup, a halogen atom, a hydroxyl group, an alkoxy group, an acyloxygroup, an amido group, a sulfonamido group, an alkoxycarbonyl group, acarboxyl group, or a sulfo group. Examples of the alkyl groups includemethyl, ethyl, propyl, butyl, isobutyl, 2-ethylhexyl, octyl, benzyl,2-phenylethyl, 2-hydroxyethyl, 3-hydroxypropyl, 2-carboxyethyl,3-carboxypropyl, 4-carboxybutyl, carboxymethyl, 2-methoxyethyl,2-(2-methoxyethoxy)ethyl, 2-sulfoethyl, 3-sulfopropyl, 3-sulfobutyl,4-sulfobutyl, 2-(3-sulfopropoxy)ethyl, 2-hydroxy-3-sulfopropyl,3-sulfopropoxyethoxyethyl, 2-acetoxyethyl, carbomethoxymethyl, and2-methanesulfonylaminoethyl.

Further, L³, L⁴, L⁵, L⁶, and L⁷ each independently represent asubstituted or unsubstituted methine group. Examples of the substituentsfor the methine group include those exemplified above as thesubstituents for the nitrogen-containing heterocyclic ring, andpreferable substituents for the methine group are the same as thosedescribed above with respect to the substituents for thenitrogen-containing heterocyclic ring. In cases where L³ to L⁷aresubstituted by substituents, the substituents may be connected with oneanother to form a five-, six-, or seven-membered ring or may form a ringwith an auxochrome. Examples of the five-, six-, and seven-memberedrings include a cyclopentene ring, a 1-dimethylaminocyclopentene ring, a1-diphenylaminocyclopentene ring, a cyclohexene ring, a1-chlorocyclohexene ring, an isophorone ring, a 1-morphorinocyclopentenering, and a cycloheptene ring.

Furthermore, n1 and n2 should preferably be such that n1 represents 0and n2 represents 1, or such that n1 represent 2 and n2 represents 0.

Also, M1 represents a charge balancing counter ion. M1 may be a cationor an anion.

Examples of the cations include an alkali metal ion, such as a sodiumion, a potassium ion, or a lithium ion; and an organic ion, such as atetraalkyl ammonium ion or a pyridinium ion.

The anion may be an inorganic anion or an organic anion Examples of theanions include a halide ion (such as a fluoride ion, a chloride ion, abromide ion, or an iodide ion), a sulfonate ion (such as amethanesulfonate ion, a trifluoromethanesulfonate ion, a methylsulfateion, a p-toluenesulfonate ion, a p-chlorobenzenesulfonate ion, a1,3-benzenedisulfonate ion, a 1,5-naphthalenedisulfonate ion, or a2,6-naphthalenedisulfonate ion), a sulfate ion, a thiocyanate ion, aperchlorate ion, a tetrafluoroborate ion, a picrate ion, an acetate ion,metal complex ions represented by the formulas shown below:

and a phosphate ion, such as a hexafluorophosphate ion or a phosphateion represented by the formula shown below:

Further, m1 represents a number necessary for keeping charge balance (atleast 0, preferably a number of 0 to 4). In cases where a salt is formedwithin the molecule, m1 represents 0. Furthermore, p and q eachindependently represent 0 or 1. Both p and q should preferably represent0.

Two kinds of the compounds, which are represented by Formula (II-1),maybe combined with each other on arbitrary carbon atoms to form a bistype of structure.

The compound represented by Formula (II-1) should preferably be acyanine dye, which is represented by Formula (II-1-1):

The cyanine dye compound represented by Formula (II-1-1) should morepreferably be a compound having the combinations described below.

It is preferred that X³ and X⁴ each independently represent an oxygenatom, —C(R³⁴)(R³⁵)—, or —N(R³⁶)—; R³² and R³³ each independentlyrepresent an unsubstituted alkyl group having 1 to 6 carbon atoms or analkyl group having 1 to 6 carbon atoms substituted with an alkoxy groupor an alkylthio group; R34, R³⁵ and R3⁶ each independently represent anunsubstituted alkyl group having from 1 to 6 carbon atoms; R³⁷represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms,which may have a substituent, a phenyl group, a pyridyl group, apyrimidyl group, a succinimido group, a benzoxazole group, or a halogenatom; Z¹¹ and Z²² each independently represent an atom group for formingan unsubstituted benzene ring, an unsubstituted naphthalene ring, or anunsubstituted quinoxaline ring, or an atom group for forming a benzenering substituted with one or two groups selected from a methyl group, achlorine atom, a fluorine atom, a methoxy group and an ethoxy group; andM2 represents a perchlorate ion, a hexafluorophosphate ion, a metalliccomplex ion represented by the following formula:

or a sulfonate ion represented by the following formula:

In Formula (II-1-1), m2 represents the valence number of M2.

In Formula (II-1-1), the most preferred combination is such that both X³and X⁴ simultaneously represent —C(R³⁴)(R³⁵)—, or —N(R³⁶)—; R³² and R³³each independently represent an unsubstituted alkyl group (such as amethyl group, an ethyl group, a propyl group, an isopropyl group, or abutyl group); R³⁴, R³⁵ and R³⁶ each independently represent a methylgroup or an ethyl group; R³⁷ represents a hydrogen atom, a methyl group,an ethyl group, a chlorine atom, or a bromine atom; and both Z¹¹ and Z²²simultaneously represent an atom group for forming an unsubstitutedbenzene ring, an unsubstituted naphthalene ring, or an unsubstitutedquinoxaline ring.

Specific examples of compounds of the chemical species capable ofproducing the fluorescence, which are represented by Formula (II-1) andmay be used in the invention, will be listed below.

No. R¹ R² R³ M B-1 CH₃ CH₃ CH₃ ClO₄ ⁻ B-2 CH₃ CH₃ C₂H₅

B-3 CH₃ CH₃ C₂H₅ PF₆ ⁻ B-4 C₂H₅ CH₃ CH₃

B-5 n-C₃H₇ CH₃ CH₃ CF₃SO₃ ⁻ B-6 n-C₄H₉ CH₃ CH₃ ClO₄ ⁻ B-7 n-C₄H₉ CH₃ CH₃

B-8 CH₂CH(CH₃)₂ CH₃ CH₃

B-9 CH₂CH₂CF₂H CH₃ CH₃ ClO₄ ⁻ B-10

CH₃ CH₃ PF₆ ⁻ B-11 CH₃ CH₃ CH₃

B-12 CH₂CH₂OC₂H₅ CH₃ CH₃ ClO₄ ⁻

No. R¹ R² R³ M B-13 n-C₄H₄ CH₃ C₂H₅ ClO₄ ⁻ B-14 n-C₄H₄ CH₃ C₂H₅ ClO₄ ⁻B-15 C₂H₅ CH₃ C₂H₅ ClO₄ ⁻

No. R¹ R² R³ R⁴ M B-16 CH₃ CH₃ CH₃ CH₃ ClO₄ ⁻ B-17 CH₃ CH₃ CH₃ CH₃

B-18 n-C₃H₇ CH₃ CH₃ CH₃ ClO₄ ⁻ B-19 n-C₄H₉ CH₃ CH₃ CH₃ ClO₄ ⁻ B-20 CH₃CH₃ CH₃

ClO₄ ⁻ B-21 CH₃ CH₃ CH₃

ClO₄ ⁻ B-22 CH₃ CH₃ CH₃

ClO₄ ⁻

No. R¹ R² R³ R⁴ M B-23 CH₃ CH₃ CH₃

ClO₄ ⁻ B-24 CH₃ CH₃ CH₃ Br ClO₄ ⁻ B-25 CH₃ CH₃ CH₃ Cl ClO₄ ⁻ B-26CH₂CO₂C₂H₅ CH₃ CH₃ H

B-27

CH₃ CH₃ H ClO₄ ⁻ B-28

CH₃ CH₃ H ClO₄ ⁻ B-29

No. R¹ R² R³ R⁴ M B-30 CH₃ CH₃ CH₃ H

B-31 CH₃ CH₃ C₂H₅ H ClO₄ ⁻ B-32 C₂H₅ CH₃ CH₃ CH₃ ClO₄ ⁻

No. R¹ R² R³ R⁴ X M B-33 C₂H₅ CH₃ CH₃

H ClO₄ ⁻ B-34 n-C₃H₇ CH₃ CH₃ H H

B-35 CH₂CH(CH₃)₂ CH₃ CH₃ H H PF₆ ⁻ B-36 n-C₄H₉ CH₃ CH₃ H CH₃ I⁻ B-37CH₂CH₂OC₂H₅ CH₃ CH₃ H Cl ClO₄ ⁻ B-38 n-C₃H₇ CH₃ CH₃ CH₃ OCH₃ ClO₄ ⁻ B-39CH₂CH(CH₃)₂ CH₃ CH₃ H SO₂NH₂ ClO₄ ⁻

No. R¹ R² R³ R⁴ X M B-40 n-C₃H₇ CH₃ CH₃ H H

B-41 n-C₄H₉ CH₃ CH₃

H ClO₄ ⁻ B-42 n-C₃H₇ CH₃ CH₃ C₂H₅ Cl PF₆ ⁻ B-43 CH₂CH(CH₃)₂ CH₃ CH₃ HCO₂C₂H₅ PF₆ ⁻ B-44 n-C₃H₇ CH₃ C₂H₅ H H ClO₄ ⁻

No. R¹ R² R³ R⁴ M B-45 n-C₃H₇ CH₃ C₂H₅ H PF₆ ⁻ B-46 C₂H₅ CH₃ C₂H₅ H ClO₄⁻ B-47 n-C₄H₉ CH₃ C₂H₅ H ClO₄ ⁻ B-48 CH₃ CH₃ C₂H₅ Br ClO₄ ⁻ B-49 CH₃ CH₃C₂H₅ Cl ClO₄ ⁻ B-50 CH₃ CH₃ C₂H₅

I⁻ B-51

No. R¹ R² R³ X M B-52 C₂H₅ C₂H₅ CH₃ H I⁻ B-53 CH₃ CH₃ H

I⁻ B-54 CH₃ CH₃ H CH₃

No. R¹ R² X M B-55 CH₃ CH₃ H I⁻ B-56 C₂H₅ C₂H₅ Br

B-57 (CH₂)₂CO₂H Br (CH₂)₂COO⁻ Na⁺ B-58

B-59

No. R¹ R² R² R⁴ M B-60 (CH₂)₄SO₃ ⁻ C₂H₅ CF₃ Cl K⁺ B-61 (CH₂)₄SO₃ ⁻ C₂H₅CN Cl K⁺ B-62

B-63

B-64

B-65

B-66

B-67

B-68

B-69

B-70

No. R¹ M B-71

ClO₄ ⁻ B-72 (CH₂)₃SCH₃ ClO₄ ⁻ B-73 (CH₂)₃SCH₃ BF₄ ⁻ B-74 (CH₂)₃SCH₃ BF₄⁻ B-75

B-76

B-77

B-78

B-79

B-80

B-81

B-82

R¹ R² R³ M n-C₄H₉ CH₃ CH₃ I⁻

The compound represented by formula (II-1) can be synthesized accordingto the methods described in Heterocyclic Compounds—Cyanine Dyes andRelated Compounds, written by F. M. Hamer, John Wiley & Sons, N.Y. andLondon (1964); Heterocyclic Compounds—Special topics in heterocyclicchemistry, written by D. M. Sturmer, John Wiley & Sons, N.Y. and London(1977), Chapter 18, Section 14, pages 482 to 515; and Rodd's Chemistryof Carbon Compounds, Elsevir Science Publishing Company Inc., 2nd. Ed.Vol. IV, Part B (1977), Chapter 15, pages 369 to 422.

In the present invention, the recording layer should more preferably beconstituted of a material comprising a combination of the chemicalspecies capable of producing the fluorescence, which is represented byFormula (II-1) shown above and a chemical species capable of quenchingthe fluorescence, which is represented by Formula (II-2) shown below.

wherein m and n each independently represent an integer of 0 to 2; X¹and X² each represent ═NR¹ or ═CR²R³, in which R¹, R², and R³ eachrepresent a substituent; and L¹ and L² each independently represent abivalent linking group.

The chemical species capable of quenching the fluorescence, which isrepresented by Formula (II-2) and which may be utilized in the presentinvention, will be described hereinbelow.

In Formula (II-2), both m and n should preferably represent 1.

Also, X¹ and X² each represent ═NR¹ or ═CR²R³. Examples of thesubstituents represented by R¹, R² and R³ include a halogen atom or asubstituent formed by combining a carbon atom, an oxygen atom, anitrogen atom and a sulfur atom, and specifically, an alkyl group, analkenyl group, an aralkyl group, an aryl group, a heterocyclic group, ahalogen atom, a cyano group, a nitro group, a mercapto group, a hydroxylgroup, an alkoxy group, an aryloxy group, an alkylthio group, anarylthio group, an acyloxy group, an amino group, an alkylamino group,an amido group, a sulfoneamido group, a sulfamoylamino group, analkoxycarbonylamino group, an alkoxysulfonylamino group, an ureidogroup, a thioureido group, an acyl group, an alkoxycarbonyl group, acarbamoyl group, an alkylsulfonyl group, an alkylsulfinyl group, asulfamoyl group, a carboxyl group (including a salt), and a sulfo group(including a salt). The above-enumerated substituents may further besubstituted with the substituents.

Examples of the substituents represented by R¹, R² and R³ will bedescribed in more detail below.

The alkyl group includes a straight-chain, branched or cyclic alkylgroup having. 1 to 18 carbon atoms (preferably 1 to 6 carbon atoms), andexamples thereof include methyl, ethyl, propyl, isopropyl, t-butyl,cyclopentyl, cyclohexyl, 2-hydroxyethyl, 3-hydroxypropyl,4-hydroxybutyl, 3-methoxypropyl, 2-aminoethyl, acetamidomethyl,2-acetamidoethyl, carboxymethyl, 2-carboxyethyl, 2-sulfoethyl,ureidomethyl, 2-ureidoethyl, carbamoylmethyl, 2-carbamoylethyl,3-carbamoylpropyl, pentyl, hexyl, octyl, decyl, undecyl, dodecyl,hexadecyl and octadecyl.

The alkenyl group include a straight-chain, branched and cyclic alkenylgroup having 2 to 18 carbon atoms (preferably 2 to 6 carbon atoms), andexamples thereof include vinyl, allyl, 1-propenyl, 2-pentenyl,1,3-butanedienyl, 2-octenyl and 3-dodecenyl.

The aralkyl group includes an aralkyl group having 7 to 10 carbon atoms,and may be, for example, benzyl.

The aryl group includes an aryl group having 6 to 10 carbon atoms, whichmay have a substituent. Examples of the aryl groups include phenyl,naphthyl, p-dibutylaminophenyl and p-methoxyphenyl.

The heterocyclic group includes a five-membered or six-memberedsaturated or unsaturated heterocyclic group comprising a carbon atom, anitrogen atom, an oxygen atom, or a sulfur atom, in which the number andthe species of the hetero atoms constituting the ring may be single orplural, and examples thereof include furil, benzofuril, pyranyl,pyrrolyl, imidazolyl, isoxazolyl, pyrazolyl, benzotriazolyl, pyridyl,pyrimidyl, pyridazinyl, thienyl, indolyl, quinolyl, phthalazinyl,quinoxalyl, pyrrolidinyl, pyrrolinyl, imidazolidinyl, imidazolinyl,pyrazolidinyl, piperidyl, piperazinyl, indolyl and morpholinyl.

Examples of the halogen atom include a fluorine atom, a chlorine atom,and a bromine atom.

The alkoxy group includes an alkoxy group having 1 to 18 carbon atoms(preferably 1 to 6 carbon atoms), which may have a substituent, and theexamples thereof include methoxy, ethoxy, propoxy, isopropoxy, butoxy,2-methoxyethoxy, 2-methanesulfonylethoxy, pentyloxy, hexyloxy, octyloxy,undecyloxy, dodecyloxy, hexadecyloxy and octadecyloxy.

The aryloxy group includes an aryloxy group having 6 to 10 carbon atoms,which may have a substituent, and examples thereof include phenoxy andp-methoxyphenoxy.

The alkylthio group includes an alkylthio group having 1 to 18 carbonatoms (preferably 1 to 6 carbon atoms), and examples thereof includemethylthio, ethylthio, octylthio, undecylthio, dodecylthio,hexadecylthio and octadecylthio.

The arylthio group includes an arylthio group having 6 to 10 carbonatoms, which may have a substituent, and examples thereof includephenylthio and 4-methoxyphenylthio.

The acyloxy group includes an acyloxy group having 1 to 18 carbon atoms(preferably 1 to 6 carbon atoms), and examples thereof include acetoxy,propanoyloxy, pentanoyloxy, octanoyloxy, dodecanoyloxy andoctadecanoyloxy.

The alkylamino group includes an alkylamino group having 1 to 18 carbonatoms (preferably 1 to 6 carbon atoms), and examples thereof includemethylamino, dimethylamino, diethylamino, dibutylamino, octylamino,dioctylamino and undecylamino.

The amido group includes an amido group having 1 to 18 carbon atoms(preferably to 6 carbon atoms), and examples thereof include acetamido,acetylmethylamino, acetyloctylamino, acetyldecylamino,acetylundecylamino, acetyloctadecylamino, propanoylamino,pentanoylamino, octanoylamino, octanoylmethylamino, dodecanoylamino,dodecanoylmethylamino and octadecanoylamino.

The sulfonamido group includes a sulfonamido group having 1 to 18 carbonatoms (preferably 1 to 6 carbon atoms), which may have a substituent,and examples thereof include methanesulfonamido, ethanesulfonamido,propylsulfonamido, 2-methoxyethylsulfonamido, 3-aminopropylsulfonamido,2-acetamidoethylsulfonamido, octylsulfonamido and undecylsulfonamido.

The alkoxycarbonylamino group includes an alkoxycarbonylamino grouphaving from 2 to 18 carbon atoms (preferably from 2 to 6 carbon atoms),and examples thereof include methoxycarbonylamino, ethoxycarbonylamino,octyloxycarbonylamino and undecyloxycarbonylamino.

The alkoxysulfonylamino group includes an alkoxysulfonylamino grouphaving from 1 to 18 carbon atoms (preferably from 1 to 6 carbon atoms),and examples thereof include methoxysulfonylamino, ethoxysulfonylamino,octyloxysufonylamino and undecyloxysulfonylamino.

The sulfamoylamino group includes a sulfamoylamino group having from 0to 18 carbon atoms (preferably from 0 to 6 carbon atoms), and examplesthereof include methylsulfamoylamino, dimethylsulfamoylamino,ethylsulfamoylamino, propylsulfamoylamino, octylsulfamoylamino andundecylsulfamoylamino.

The ureido group includes an ureido group having from 1 to 18 carbonatoms (preferably from 1 to 6 carbon atoms), which may have asubstituent, and examples thereof include ureido, methylureido,N,N-dimethylureido, octylureido and undecylureido.

The thioureido group includes a thioureido group having from 1 to 18carbon atoms (preferably from 1 to 6 carbon atoms), which may have asubstituent, and examples thereof include thioureido, methylthioureido,N,N-dimethylthioureido, octylthioureido and undecylthioureido.

The acyl group includes an acyl group having from 1 to 18 carbon atoms(preferably from 1 to 6 carbon atoms), and examples thereof includeacetyl, benzoyl, octanoyl, decanoyl, undecanoyl and octadecanoyl.

The alkoxycarbonyl group includes an alkoxycarbonyl group having from 2to 18 carbon atoms (preferably from 2 to 6 carbon atoms), and examplesthereof include methoxycarbonyl, ethoxycarbonyl, octyloxycarbonyl andundecyloxycarbonyl.

The carbamoyl group includes a carbamoyl group having from 1 to 18carbon atoms (preferably from 1 to 6 carbon atoms), which may have asubstituent, and examples thereof include carbamoyl,N,N-dimethylcarbamoyl, N-ethylcarbamoyl, N-octylcarbamoyl,N,N-dioctylcarbamoyl and N-undecylcarbamoyl.

The alkylsulfonyl group includes an alkylsulfonyl group having from 1 to18 carbon atoms (preferably from 1 to 6 carbon atoms), which may have asubstituent, and examples thereof include methanesulfonyl,ethanesulfonyl, 2-chloroethanesulfonyl, octanesulfonyl andundecanesulfonyl.

The alkylsulfinyl group includes an alkylsulfinyl group having from 1 to18 carbon atoms (preferably from 1 to 6 carbon atoms), and examplesthereof include methanesuflinyl, ethanesulfinyl and octanesulfinyl.

The sulfamoyl group includes a sulfamoyl group having from 0 to 18carbon atoms (preferably from 0 to 6 carbon atoms), which may have asubstituent, and examples there,of include sulfamoyl, dimethylsulfamoyl,ethylsulfamoyl, octylsulfamoyl, dioctylsulfamoyl and undecylsulfamoyl.

Further, L¹ and L² each independently represent a bivalent linkinggroup. The bivalent linking group used herein comprises a carbon atom, anitrogen atom, an oxygen atom, or a sulfur atom, and constitutes afour-membered to eight-membered ring together with the carbon atoms, towhich X¹ and X² are connected.

Specific examples of L¹ and L²include a bivalent linking groupconstituted by combining —C(R⁴)(R5)—, —C(R⁶)═, —N(R⁷)—, —N═, —O— and—S—, in which R⁴, R⁵, R⁶ and R⁷ each independently represent a hydrogenatom or a substituent, the details of which are the same as thosedescribed for R¹, R² and R³. The four-membered to eight-membered ringmay form a saturated or unsaturated condensed ring, and examples of thecondensed ring include a cycloalkyl ring, an aryl ring and aheterocyclic ring, the details of which are the same as those describedabove for R¹, R² and R³.

The four-membered to eight-membered ring will be described in moredetail below.

Examples of the four-membered ring include cyclobutanedione,cyclobutenedione and benzocyclobutenequinone.

Examples of the five-membered ring include cyclopentanedione,cyclopentenedione, cyclopentanetrione, cyclopentenetrione, indandione,indantrione, tetrahydrofurandione, tetrahydrofurantrione,tetrahydropyrroledione, tetrahydropyrroletrione,tetrahydrothiophenedione and tetrahydrothiophenetrione.

Examples of the six-membered ring include benzoquinone, quinomethane,quinodimethane, quinoneimine, quinonediimine, thiobenzoquinone,dithiobenzoquinone, naphthoquinone, anthraquinone,dihydrochromenetrione, dihydropyridinedione, dihydropyrazinedione,dihydropyrimidinedione, dihydropyridazinedione, dihydrophthalazinedione,dihydroisoquinolinedione and tetrahydroquinolinetrione.

Examples of the seven-membered ring include cycloheptanedione,cycloheptanetrione, azacycloheptanetrione, diazacycloheptanetrione,oxocycloheptanetrione, dioxocycloheptanetrione andoxoazacycloheptanetrione.

Examples of the eight-membered ring include cyclooctanedione,cyclooctanetrione, azacyclooctanetrione, diazacyclooctanetrione,oxocyclooctanetrione, dioxocyclooctanetrione, oxoazacyclooctanetrione,cyclooctenedione, cyclooctadienedione and dibenzocyclooctenedione.

The ring formed by L¹ and L² together with the carbon atoms, to which X¹and X² are connected, is preferably a six-membered ring.

The chemical species capable of quenching the fluorescence should morepreferably be a compound represented by Formula (II-2-1) shown below.

wherein ═NR⁸ and ═CR⁹R¹⁰ represented by X¹¹ and X²² have the samemeanings as ═NR¹ and ═CR²R³ represented by X¹ and X² in Formula (II-2),and the preferred scopes thereof are also the same; and the substituentsrepresented by R³, R⁹ and R¹⁰ have the same meanings as the substituentsrepresented by R¹, R² and R³ in Formula (II-2), and the preferred scopesthereof are also the same.

R¹¹, R¹², R¹³ and R¹⁴ each independently represent a hydrogen atom or asubstituent. When R¹¹ and R¹², or R¹³ and R¹⁴ are the substituents atthe same time, these may be connected to each other to form anunsaturated condensed ring. The unsaturated condensed ring may have asubstituent, and examples of the substituent include those exemplifiedfor R¹ to R³.

X¹¹ and X²² each independently preferably represent an oxygen atom or a═CR⁹R¹⁰ group, and more preferably these simultaneously represent oxygenatoms or simultaneously represent ═CR⁹R¹⁰ groups. R⁹and R¹⁰ eachindependently preferably represent a halogen atom, a cyano group, anacyl group, an alkoxycarbonyl group or an alkylsulfonyl group.

The cases where X¹¹ and X²² simultaneously represent oxygen atoms willbe described hereinbelow.

In cases where X¹¹ and X²² simultaneously represent oxygen atoms, it ispreferred that at least two of R¹¹, R¹², R¹³ and R¹⁴ are electronattracting groups. The electron attracting group herein means asubstituent having a positive Hammett's op value, and specificallyexamples thereof include a halogen atom, a cyano group, a nitro group,an acyl group, an alkoxycarbonyl group, a carbamoyl group, analkylsulfonyl group and an alkylsulfinyl group.

In cases where X¹¹ and X²² simultaneously represent oxygen atoms, it isparticularly preferred that R¹¹, R¹², R¹³ and R¹⁴ each independentlyrepresent a hydrogen atom, an alkyl group, a halogen atom, a cyanogroup, a nitro group, an alkoxy group, an alkylthio group, an aminogroup, an alkylamino group, an amido group, a sulfonamido group, asulfamoylamino group, an alkoxycarbonylamino group, analkoxysulfonylamino group, an ureido group, a thioureido group, an acylgroup, an alkoxycarbonyl group, a carbamoyl group, an alkylsulfonylgroup, an alkylsulfinyl group and a sulfamoyl group, provided that atleast two of them are electron attracting groups.

As the most preferred combination, R¹¹, R¹², R¹³ and R¹⁴ eachindependently represent a hydrogen atom, an alkyl group having from 1 to6 carbon atoms, a halogen atom, a cyano group, an alkoxy group havingfrom 1 to 6 carbon atoms, an alkylthio group having from 1 to 6 carbonatoms, an amido group having from 1 to 6 carbon atoms, a sulfoneamidogroup having from 1 to 6 carbon atoms, an ureido group having from 1 to6 carbon atoms, an acyl group having from 1 to 6 carbon atoms, analkoxycarbonyl group having from 2 to 6 carbon atoms, a carbamoyl grouphaving from 1 to 6 carbon atoms, an alkylsulfonyl group having from 1 to6 carbon atoms or an alkylsulfinyl group having from 1 to 6 carbonatoms, provided that at least two of them are a halogen atom, a cyanogroup, an alkylsulfonyl group or an alkylsulfinyl group.

In cases where X¹¹ and X²² simultaneously represent ═CR⁹R¹⁰ groups, thechemical species capable of quenching the fluorescence shouldparticularly preferably be a compound represented by Formula (II-2-2)shown below.

wherein R¹⁵, R¹⁶, R¹⁷ and R¹⁸ each independently have the same meaningsas those described for R¹¹ to R¹⁴.

The chemical species capable of quenching the fluorescence should mostpreferably be a compound represented by Formula (II-2-3) or (II-2-4)shown below.

In Formula (II-2-3), R¹⁹ represents a halogen atom, a cyano group, analkoxy group, an alkylthio group, an amido group, a sulfoneamido group,an ureido group, an acyl group or an alkoxycarbonyl group; R²⁰ has thesame meaning as those explained above for R¹ to R³; and m4 represents aninteger of from 1 to 4, provided that, in cases where m4 or 4-m4represents an integer of at least 2, the at least two R¹⁹ may beidentical or different, and the at least two R²⁰ may be identical ordifferent.

In Formula (II-2-4), R²¹ represents a hydrogen atom or a substituent.The substituent herein has the same meaning as explained above for R¹ toR³, and m5 represents an integer of from 0 to 6, provided that, in caseswhere m5 represents an integer of 2 or more, a plurality of R²¹ may beidentical or different.

A preferred combination of R¹⁹ and R²⁰ in Formula (II-2-3) will bedescribed below.

A combination, in which R¹⁹ represents a halogen atom, a cyano group, analkoxy group having from 1 to 6 carbon atoms, an acyl group having from1 to 8 carbon atoms or an alkoxycarbonyl group having from 2 to 6 carbonatoms, and R²⁰ represents a hydrogen atom or an alkyl group having from1 to 6 carbon atoms, is preferred, and the most preferred combination isthat R¹⁹ represents an alkoxy group having from 1 to 6 carbon atoms, andR²⁰represents a hydrogen atom.

The chemical species capable of quenching the fluorescence, which isrepresented by Formula (II-2-3) should particularly preferably be acompound represented by the following formula:

In Formula (II-2-4), R²¹ preferably represents a hydrogen atom, an alkylgroup, a halogen atom, a cyano group, an alkoxy group, an alkylthiogroup, an amido group, a sulfoneamido group, an ureido group or an acylgroup; more preferably a halogen atom, an alkyl group having from 1 to 6carbon atoms, a halogen atom, a cyano group, an alkoxy group having from1 to 6 carbon atoms, an alkylthio group having from 1 to 6 carbon atoms,an amido group having from 1 to 6 carbon atoms, a sulfoneamido grouphaving from 1 to 6 carbon atoms, an ureido group having from 1 to 6carbon atoms or an acyl group having from 1 to 6 carbon atoms;particularly preferably a hydrogen atom, an alkyl group having from 1 to6 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, acyano group or an alkoxy group having from 1 to6carbon atoms; and mostpreferably a hydrogen atom.

Specific examples of the compounds of the chemical species capable ofquenching the fluorescence, which may be utilized in the presentinvention, will be described below.

No. R¹ R² R³ R⁴ A-1  H H H H A-2  CH₃ H H H A-3  CH₃ H OCH₃ H A-4  OCH₃H OCH₃ H A-5  C₁₈H₃₇ H H H A-6  F H H H A-7  Cl H H H A-8  Br H H H A-9 OCH₃ H H H A-10 CH₂Ph H H H A-11 CH₂CO₂H H H H A-12 OC₂H₅ H OC₂H₅ H A-13OC₂H₅ H SCH₃ H A-14 Cl H Cl H A-15 CH₃ H Br H A-16 CH₃ H CH₃ H A-17CO₂CH₃ H H H A-18 COC₁₁H₂₃ H H H A-19 Br H OCH₂CH₂OH H

No. R¹ R² R³ R⁴ A-20 CH₃ CH₃ CH₃ CH₃ A-21 CH₃ OCH₃ CH₃ OCH₃ A-22 F H F HA-23 F F F F A-24 CN H CN H A-25 CO₂CH₃ H CO₂CH₃ H A-26 Cl NHCOC₁₁H₂₃ ClNHCOC₁₁H₂₃ A-27

No. R¹ R² R³ R⁴ R⁵ R⁶ A-28 CH₃ H H H H H A-29 CH₃ Cl H H H H A-30 CH₃CH₃ H H H H A-31 H H H OCH₃ H H A-32 H H H C₈H₁₇ H H A-33 H H H SCH₃ H HA-34

A-35

A-36

A-37

A-38

A-39

A-40

No. R¹ R² R³ R⁴ A-41 H H H H A-42 H CO₂CH₃ H H A-43

A-44

A-45

A-46

A-47

A-48

A-49

A-50

A-51

No. R¹ R¹ R³ R⁴ A-52 Cl Cl Cl Cl A-53 Cl H Cl H A-54 F F F F A-55 Cl ClCl NHCOCH₃ A-56 Cl Cl Cl

A-57 Cl NHCOC₅H₁₁ Cl NHCOC₅H₁₁ A-58 Cl NHCOC₁₁H₂₃ Cl NHCOC₁₁H₂₃ A-59 ClNHCONHC₂H₅ Cl NHCONHC₂H₅ A-60 Cl NHSO₂CH₃ Cl NHSO₂CH₃

No. R¹ R² R³ R⁴ A-61 Cl CO₂C₂H₅ Cl CO₂C₂H₅ A-62 Cl CONHC₈H₁₇ ClCONHC₈H₁₇ A-63 Cl H SC₂H₅ H A-64 H H H H A-65 CO₂C₂H₅ CO₂C₂H₅ CO₂C₂H₅CO₂C₂H₅ A-66 CO₂C₂H₅ H CO₂C₂H₅ H A-68 SC₁₂H₂₅ H H H A-69 Cl Cl CN CNA-70

A-71

A-72

A-73

A-74

No. R¹ R² R³ R⁴ A-75 SO₂C₂H₅ SO₂C₂H₅ SO₂C₂H₅ SO₂C₂H₅ A-76 SO₂C₂H₅SO₂C₂H₅ SO₂C₂H₅ OC₂H₅ A-77 SO₂C₂H₅ OC₂H₅ SO₂C₂H₅ OC₂H₅ A-78 SO₂C₂H₅ HSO₂C₂H₅ H A-79 C₂H₅ SOC₂H₅ SOC₂H₅ SOC₂H₅ A-80 SO₂Ph SO₂Ph SO₂Ph Cl A-81SO₂Ph SO₂Ph CN CN A-82 SO₂Ph SO₂Ph SO₂Ph SO₂Ph A-83 SCF₃ SCF₃ SCF₃ SCF₃A-84 SOCF₃ SOCF₃ SOCF₃ SOCF₃ A-85 SO₂CF₃ SO₂CF₃ SO₂CF₃ SO₂CF₃ A-86SO₂CF₃ H SO₂CF₃ H A-87 H H SO₂CF₃ H A-88 Cl SO₂CF₃ SO₂CF₃ Cl A-89

A-90

A-91

A-92

A-93

A-94

A-95

A-96

A-97

A-98

A-99

A-100

A-101

A-102

A-103

A-104

A-105

A-106

A-107

A-108

A-109

A-110

A-111

A-112

A-113

A-114

A-115

A-116

A-117

A-118

A-119

A-120

No. X¹ X² A-121 NC₈H₁₇ NC₈H₁₇ A-122 N + (C₅H₁₁)₂ O A-123

A-124

No. R¹ R² R³ R⁴ A-125 CN CO₂CH₃ CN CO₂CH₃ A-126 CN CO₂C₄H₉ CN CO₂C₄H₉A-127 CN CO₂C₁₁H₂₃ CN CO₂C₁₁H₂₃ A-128 CO₂C₂H₅ CO₂C₂H₅ CO₂C₂H₅ CO₂C₂H₅A-129 COCH₃ COCH₃ COCH₃ COCH₃ A-130 SO₂C₂H₅ SO₂C₂H₅ SO₂C₂H₅ SO₂C₂H₅A-131 Cl Cl CN CN

No. R¹ R² R³ R⁴ A-132 H H H H A-133 Cl Cl Cl Cl A-134 Cl H Cl H A-135

A-136

A-137

A-138

A-139

A-140

A-141

A-142

A-143

A-144

A-145

A-146

A-147

The compound represented by Formula (II-2) can be easily synthesizedaccording to a general synthesis method described, for example, in J.Chem. Soc. Perkin Trans. 1, 611 (1992) and Synthesis, 546 (1971).Furthermore, the following synthesis example and a method accordingthereto may be employed.

SYNTHESIS EXAMPLE

The example compound (A-22) according to the invention was synthesizedby the following scheme:

Synthesis of (A-22a)

Firstly, 2.72 g of 1,4-dibromo-2,5-difluorobenzene, 24.9 g of potassiumiodide, 9.53 g of copper iodide and 30 ml of HMPA 20(hexamethylphosphoric triamide) were mixed, and heated to 150 to 160° C.in a nitrogen atmosphere. After completing the reaction, diluted aqueoushydrochloric acid and ether were poured into the reaction liquid, andafter filtration of a copper salt, an organic layer was extracted. Theorganic layer was washed with aqueous sulfite, and after drying withsodium sulfate, the organic layer was filtered. The filtrate wasconcentrated under reduced pressure to obtain 2.93 g of (A-22a) asyellow crystals.

Synthesis of (A-22b)

Firstly, 60 ml of THF (tetrahydrofuran) was added to 3.66 g of (A-22a),2.64 g of malononitrile, 1.44 g of sodium hydroxide and 0.21 g ofbistriphenylphosphine palladium chloride, and then heated while beingrefluxed for 12 hours. After completing the reaction, the reactionliquid was poured into 1 N hydrochloric acid, and a white precipitatethus formed was filtered, followed by drying, to obtain 2.68 g of(A-22b) as a white solid.

Synthesis of (A-22)

Firstly, 100 ml of water was added to 3.36 g of (A-22b), and anexcessive amount of bromine water was gradually added dropwise into theresulting suspension. After the mixture was allowed to stand overnight,the resulting red precipitate was filtered, and after washing with coldwater, it was dissolved in 60 ml of methylene chloride. After theresulting solution was dried by use of sodium sulfate, it was treatedwith activated charcoal, and the solvent was distilled out to obtain3.11 g of the objective example compound (A-22) as yellow crystals.

The example compound (A-58) according to the invention was synthesizedby the following scheme:

Synthesis of (A-58a)

Firstly, 25.0 g of chloranil was dissolved in 60 ml of acetonitrile, andan ammonia gas was continuously introduced into the resultingsuspension. The resulting brown solid was filtered and washed with waterand then with 100 ml of acetonitrile, and then dried under reducedpressure to obtain 19.6 g of (A-58a).

Synthesis of (A-58)

Firstly, 100 ml of DMF was added to 2.1 g of (A-58a), 4.4 g of laurylicacid chloride and 2.8 ml of triethylamine, and heated to 70° C. Afterheating for 7 hours, the reaction liquid was poured into 300 ml of coldwater, and then extracted with ethyl acetate. After drying the resultingsolution by use of sodium sulfate, it was concentrated andrecrystallized from acetonitrile to obtain 1.7 g of the example compound(A-58) as yellow crystals.

The chemical species capable of quenching the fluorescence, which isrepresented by Formula (II-2) may be used singly or in combination withother known quenchers.

Representative examples of the other quenchers used in combinationinclude the metallic complex, the diimmonium salt and the aminium saltrepresented by formulae (III), (IV) and (V) described in JapaneseUnexamined Patent Publication No. 3(1991)-224793, and the nitrosocompound shown in Japanese Unexamined Patent Publication No.2(1990)-300287 and No. 2(1990)-300288. The quencher to be combined isparticularly preferably a metallic complex (for example, PA-1006 (MitsuiToatsu Fine chemicals Co., Ltd.)) and a diimmonium salt (for example,IRG-023 and IRG-022 (Nippon Kayaku Co., Ltd.)), and most preferably adiimmonium salt These quenchers may be used in combination of two ormore thereof, depending on the object.

The addition amount of the chemical species capable of quenching thefluorescence, which is represented by Formula (II-2), is preferably inthe range of from 1 to 100 parts by weight per 100 parts by weight ofthe chemical species capable of producing the fluorescence, morepreferably from 1 to 50 parts by weight, particularly preferably from 1to 25 parts by weight, and most preferably from 1 to 10 parts by weight.

The addition amount of the other quencher is preferably in the range offrom 1 to 100 parts by weight per 100 parts by weight of the chemicalspecies capable of producing the fluorescence, more preferably from 1 to50 parts by weight, particularly preferably from 1 to 25 parts byweight, and most preferably from 1 to 10 parts by weight.

Another preferable combination of the chemical species represented byFormula (II) is the combination, in which the chemical species [FL] isan anion represented by Formula (II-3) shown below, and the chemicalspecies [Q] is a cation represented by Formula (II-4), which will bedescribed later. The anion is represented by Formula (II-3) shown below.

wherein Za and Zb each independently represent an atom group necessaryfor forming a five-membered or six-membered, nitrogen-containingheterocyclic ring; R¹ and R² each independently represent an alkyl groupor an aryl group; L¹, L², L³, L⁴, and L⁵ each independently represent asubstituted or unsubstituted methine group, provided that, in caseswhere L¹ to L⁵ are substituted by substituents, the substituents mayoptionally be connected with one another to form a ring; n represents aninteger of at least 1; j represents 0, 1, or 2; and k represents 0 or 1.

Examples of the five-membered or six-membered nitrogen-containingheterocyclic ring (nucleus) represented by Za and Zb include a thiazolenucleus, a benzothiazole nucleus, a naphthothiazole nucleus, athiazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, anaphthoxazole nucleus, an oxazoline nucleus, a selenazole nucleus, abenzoselenazole nucleus, a naphthoselenazole nucleus, a selenazolinenucleus, a tellurazole nucleus, a benzotellurazole nucleus, anaphthotellurazole nucleus, a tellurazoline nucleus, an imidazolenucleus, a benzoimidazole nucleus, a naphthoimidazole nucleus, apyridine nucleus, a quinoline nucleus, an isoquinoline nucleus, animidazo [4,5-b] quinoxaline nucleus, an oxadiazole nucleus, athiadiazole nucleus, a tetrazole nucleus, and a pyrimidine nucleus.

Among these, a benzothiazole nucleus, an imidazole nucleus, anaphthoimidazole nucleus, a quinoline nucleus, an isoquinoline nucleus,an imidazo [4,5-b] quinoxaline nucleus, a thiadiazole nucleus, atetrazole nucleus, and a pyrimidine nucleus are preferred.

These rings may have a benzene ring or a naphthoquinone ring condensedtherewith.

The five-membered or six-membered nitrogen-containing heterocyclic ringmay have a substituent. Preferred examples of the substituent include ahalogen atom, a substituted or unsubstituted alkyl group, and an arylgroup. As a halogen atom, a chlorine atom is preferred. As an alkylgroup, a straight-chain alkyl group having from 1 to 6 carbon atoms ispreferred. Examples of the substituent on the alkyl group include analkoxy group (such as methoxy) and an alkylthio group (such asmethylthio). As an aryl group, a phenyl group is preferred.

The alkyl group represented by R¹ and R² may have a substituent.Preferred examples thereof include a straight-chain, cyclic or branchedalkyl group having from 1 to 18 (more preferably from 1 to 8, andparticularly from 1 to 6) carbon atoms.

The aryl group represented by R¹ and R² may have a substituent, and ispreferably an aryl group having from 6 to 18 carbon atoms, which mayhave a substituent.

Preferred examples of the substituent of the alkyl group or the arylgroup represented by R¹ and R² include a substituted or unsubstitutedaryl group having from 6 to 18 carbon atoms (such as phenyl,chlorophenyl, anisyl, toluyl, 2,4-di-t-amyl, and 1-naphthyl), an alkenylgroup (such as vinyl and 2-methylvinyl), an alkynyl group (such asethynyl, 2-methylethynyl, and 2-phenylethynyl), a halogen atom (such asF, Cl, Br, and I), a cyano group, a hydroxyl group, a carboxyl group, anacyl group (such as acetyl, benzoyl, salicyloyl, and pivaloyl), analkoxy group (such as methoxy, butoxy, and cyclohexyloxy), an aryloxygroup (such as phenoxy and 1-naphthoxy), an alkylthio group (such asmethylthio, butylthio, benzylthio, and 3-methoxypropylthio), an arylthiogroup (such as phenylthio and 4-chlorophenylthio), an alkylsulfonylgroup (such as methanesulfonyl and butanesulfonyl), an arylsulfonylgroup (such as benzensulfonyl and paratoluenesulfonyl), a carbamoylgroup having from 1 to 10 carbon atoms, an amido group having from 1 to10 carbon atoms, an acyloxy group having from 2 to 10 carbon atoms, analkoxycarbonyl group having from 2 to 10 carbon atoms, a heterocyclicgroup (such as a heterocyclic aromatic ring, e.g., pyridyl, thienyl,furyl, thiazolyl, imidazolyl and pyrazolyl, and an aliphaticheterocyclic ring, e.g., a pyrrolidine ring, a piperidine ring, amorphorine ring, a pyran ring, a thiopyran ring, a dioxane ring and adithiolane ring).

In the invention, R¹ and R² are each preferably a straight-chain alkylgroup having from 1 to 8 (preferably from 1 to 6, and particularly from1 to 4) carbon atoms having, as a substituent, an unsubstitutedstraight-chain alkyl group having from 1 to 8 (preferably from 1 to 6,and particularly from 1 to 4) carbon atoms, an unsubstituted alkoxygroup (particularly methoxy), or an unsubstituted alkylthio group(particularly methylthio).

The methine group represented by L¹ to L⁵ may have a substituent.Preferred examples of the substituent include an alkyl group having from1 to 18 carbon atoms, an aralkyl group, and those exemplified as thepreferred examples of the substituent for the alkyl group or the arylgroup represented by R¹ and R². Among these, an alkyl group (such asmethyl), an aryl group (such as phenyl), a halogen atom (such as Cl andBr), and an aralkyl group (such as benzyl) are preferred.

In the invention, j and k are preferably each independently 0 or 1.

The substituents on L¹ to L⁵ may be connected to form a ring. The ringis preferably a five-membered ring or a six-membered ring, and two ormore of the rings may be condensed with each other. The positions atwhich the rings are connected are different depending on the number ofthe methine chain. For example, in the case where the methine chainformed with L¹ to L⁵ is a pentamethine chain, the preferred connectingpositions are L¹ and L³, L² and L⁴, and L³ and L⁵. The connectingposition in the case of forming a double condensed ring is preferablyL¹, L³ and L⁵. In this case, L¹ and R¹, L⁵ and R², and L³ and R² mayeach be connected to form a ring, which is preferably a five-memberedring or a six-membered ring.

In the invention, the ring formed with the substituents on L¹ to L⁵ ispreferably a cyclohexene ring.

Among the anions represented by Formula (II-3), an anion represented byFormula (II-3-1) is more preferred.

wherein Z¹ and Z² each independently represent an atomic group forforming an indolenine nucleus or a benzoindolenine nucleus; R¹ and R²each independently represent an alkyl group or an aryl group, R³, R⁴, R⁵and R⁶ each independently represent an alkyl group; L¹, L², L³, L⁴ andL⁵ each independently represent a substituted or unsubstituted methinegroup (provided that when L¹ to L⁵ have substituents, they may beconnected to form a ring); n represents an integer of at least 1; jrepresents 0, 1 or 2; and k represents 0 or 1.

The indolenine nucleus or the benzoindolenine nucleus represented by Z¹and Z² may have a substituent. Examples of the substituent (atom)include a halogen atom and an aryl group. As a halogen atom, a chlorineatom is preferred. As an aryl group, a phenyl group is preferred.

The alkyl group represented by R³, R⁴, R⁵and R⁶ is preferably astraight-chain, branched or cyclic alkyl group having from 1 to 18carbon atoms. R³ and R⁴, R⁵ and R⁶ may be connected to each other toform a ring.

The alkyl group represented by R³, R⁴, R⁵ and R⁶ may have a substituent.Preferred examples of the substituent include those exemplified as thepreferred substituents for the alkyl group or the aryl group representedby R¹ and R².

In the invention, the alkyl group represented by R³, R⁴, R⁵ and R⁶ ispreferably a straight-chain unsubstituted alkyl group having from 1 to 6carbon atoms (particularly methyl and ethyl).

In Formula (II-3-1), R¹, R², L¹, L², L³, L⁴, L⁵, j, k, and n have thesame meanings as those in Formula (II-3). Preferred examples thereof arealso the same as those in Formula (II-3).

The (SO₃ ⁻) group in —(SO₃ ⁻)_(n+1) is preferably connected to the endof R¹ and R² in Formula (II-3) and Formula (II-3-1).

Specific examples in Formula (II-3) will be listed below.

The cation represented by Formula (II-4) will be described hereinbelow.The cation is represented by the formula shown below.

wherein R₅ and R₆ each independently represent a substituent group; R₇and R₈ each independently represent an alkyl group, an alkenyl group, analkynyl group, an aralkyl group, an aryl group or a heterocyclic group,provided that R₅ and R₆, R₅ and R₇, R₆ and R₈, or R₇ and R₈ may beconnected with each other to form a ring; and r and s each independentlyrepresent an integer of 0 to 4, provided that, in cases where r and seach represent an integer of at least 2, the at least two substituentsR₅ may be identical or different, and the at least two substituents R₆maybe identical or different.

As the alkyl group represented by R₇ and R₈, a substituted orunsubstituted alkyl group having from 1 to 18 carbon atoms is preferred,and more preferably a substituted or unsubstituted alkyl group havingfrom 1 to 8 carbon atoms. The alkyl group may be straight-chain,branched or cyclic. Examples thereof include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, t-butyl, n-hexyl, neopentyl, cyclohexyl,adamantyl, and cyclopropyl.

Examples of the substituent for the alkyl group include the following:

a substituted or unsubstituted alkenyl group having from 2 to 18 carbonatoms (preferably from 2 to 8 carbon atoms) (such as vinyl);

a substituted or unsubstituted alkynyl group having from 2 to 18 carbonatoms (preferably from 2 to 8 carbon atoms) (such as ethynyl);

a substituted or unsubstituted aryl group having from 6 to 10 carbonatoms (such as phenyl and naphthyl);

a halogen atom (such as F, Cl and Br);

a substituted or unsubstituted alkoxy group having from 1 to 18 carbonatoms (preferably from 1 to 8 carbon atoms) (such as methoxy andethoxy);

a substituted or unsubstituted aryloxy group having from 6 to 10 carbonatoms (such as phenoxy and p-methoxyphenoxy);

a substituted or unsubstituted alkylthio group having from 1 to 18carbon atoms (preferably from 1 to 8 carbon atoms) (such as methylthoand ethylthio);

a substituted or unsubstituted arylthio group having from 6 to 10 carbonatoms (such as phenylthio);

a substituted or unsubstituted acyl group having from 2 to 18 carbonatoms (preferably from 2 to 8 carbon atoms) (such as acetyl andpropyonyl);

a substituted or unsubstituted alkylsulfonyl group or arylsulfonyl grouphaving from 1 to 18 carbon atoms (preferably from 1 to 8 carbon atoms)(such as methanesulfonyl and p-toluenesulfonyl);

a substituted or unsubstituted acyloxy group having from 2 to 18 carbonatoms (preferably 2 to 8 carbon atoms) (such as acetoxy andpropionyloxy);

a substituted or unsubstituted alkoxycarbonyl group having from 2 to 18carbon atoms (preferably from 2 to 8 carbon atoms) (such asmethoxycarbonyl and ethoxycarbonyl);

a substituted or unsubstituted aryloxycarbonyl group having from 7 to 11carbon atoms (such as naphthoxycarbonyl);

an unsubstituted amino group, or a substituted amino group having from 1to 18 carbon atoms (preferably from 1 to 8 carbon atoms) (such asmethylamino, dimethylamino, diethylamino, anilino, methoxyphenylamino,chlorophenylamino, pyridylamino, methoxycarbonylamino,n-butoxycarbonylamino, phenoxycarbonylamino, methylcarbamoylamino,ethylthiocarbamoylamino, phenylcarbamoylamino, acetylamino,ethylcarbonylamino, ethylthiocarbamoylamino, cyclohexylcarbonylamino,benzoylamino, chloroacetylamino, and methylsulfonylamino);

a substituted or unsubstituted carbamoyl group having from 1 to 18carbon atoms (preferably from 1 to 8 carbon atoms) (such asunsubstituted carbamoyl, methylcarbamoyl, ethylcarbamoyl,n-butylcarbamoyl, t-butylcarbamoyl, dimethylcarbamoyl,morphorinocarbamoyl, and pyrrolidinocarbamoyl);

an unsubstituted sulfamoyl group, or a substituted sulfamoyl grouphaving from 1 to 18 carbon atoms (preferably from 1 to 8 carbon atoms)(such as methylsulfamoyl and phenylsulfamoyl) a cyano group, a nitrogroup, a carboxyl group, and a hydroxyl group; and

a heterocyclic group (such as an oxazole ring, a benzoxazole ring, athiazole ring, a benzothiazole ring, an imidazole ring, a benzoimidazolering, an indolenine ring, a pyridine ring, a piperidine ring, apyrrolidine ring, a morphorine ring, a sulfolane ring, a furan ring, athiophene ring, a pyrazole ring, a pyrrole ring, a chroman ring, and acoumarin ring).

As the alkenyl group represented by R₇ and R₈, a substituted orunsubstituted alkenyl group having from 2 to 18 carbon atoms, and morepreferably a substituted or unsubstituted alkenyl group having from 2 to8 carbon atoms, such as vinyl, allyl, 1-propenyl, and 1,3-butadienyl isused.

As the substituent for the alkenyl group, those exemplified above as thesubstituents for the alkyl group are preferred.

As the alkynyl group represented by R₇ and R₈, a substituted orunsubstituted alkynyl group having from 2 to 18 carbon atoms, and morepreferably a substituted or unsubstituted alkynyl group having from 2 to8 carbon atoms, such as ethynyl and 2-propynyl is used.

As the substituent for the alkynyl group, those exemplified above as thesubstituents for the alkyl group are preferred.

As the aralkyl group represented by R₇ and R₈, a substituted orunsubstituted aralkyl group having from 7 to 18 carbon atoms, such asbenzyl and methylbenzyl are preferred.

As the aryl group represented by R₇ and R₈, a substituted orunsubstituted aryl group having from 6 to 18 carbon atoms, such asphenyl or naphthyl, is preferred.

As the substituent for the aryl group, those exemplified above as thesubstituents for the alkyl group are preferred in addition to these, analkyl group (such as methyl and ethyl) is also preferred.

The heterocyclic group represented by R₇ and R₈ includes a saturated orunsaturated five-membered or six-membered heterocyclic ring constitutedwith a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom,and examples thereof include an oxazole ring, a benzoxazole ring, athiazole ring, a benzothiazole ring, an imidazole ring, a benzoimidazolering, an indolenine ring, a pyridine ring, a piperidine ring, apyrrolidine ring, a morphorine ring, a sulfolane ring, a furan ring, athiophene ring, a pyrazole ring, a pyrrole ring, a chroman ring, and acoumarin ring. The heterocyclic group may have a substituent, and as thesubstituent in this case, those exemplified above as the substituentsfor the alkyl group are preferred.

The substituent represented by R₅ and R₆ is the same as thoseexemplified as the substituents for the alkyl group. In addition tothese, an alkyl group (such as methyl and ethyl) is also exemplified.

In the invention, the substituent represented by R₅ and R₆ is preferablya hydrogen atom or an alkyl group, and particularly preferably ahydrogen atom.

The partial structure represented by Formula (II-4) is particularlypreferably the one represented by Formula (II-4-1) or (II-4-2) shownbelow.

wherein R₁₇ and R₁₈ have the same meanings as the substituentsrepresented by R₅ and R₆ described above, and the preferred scopesthereof are also the same; R₁₉ and R₂₀ have the same meanings as thesubstituents represented by R₇ and R₈, and the preferred scopes thereofare also the same; and r and s each independently represent an integerof from 0 to 4, provided that when r and s are 2 or more, plural groupsrepresented by r and s may be the same or different.

wherein R₂₁ and R₂₂ have the same meanings as the substituentsrepresented by R₅ and R₆ described above, and the preferred scopesthereof are also the same, R₂₁ and R₂₂ are preferred to be connected toeach other to form a carbon ring or a heterocyclic ring, and areparticularly preferred to be a condensed aromatic ring combined with thepyridine ring, to which R₂₁ and R₂₂ are connected; and r and s eachindependently represent an integer of from 0 to 4, provided that when rand s are 2 or more, plural groups represented by r and s may be thesame or different.

Specific examples of the part represented by Formula (II-4) in thecompound represented by Formula (II) used in the invention will belisted below.

No. R¹ R² B-1  CH₃ CH₃ B-2  C₂H₅ C₂H₅ B-3  n-C₃H₇ n-C₃H₇ B-4  n-C₄H₉n-C₄H₉ B-5  iso-C₄H₉ iso-C₄H₉ B-6  n-C₆H₁₃ n-C₆H₁₃ B-7  —C(CH₃)₃—C(CH₃)₃ B-8  —CH₂CH₂C(CH₃)₃ —CH₂CH₂C(CH₃)₃ B-9  CH₂═CH CH₂═CH B-10NCCH₂ NCCH₂ B-11 EtO₂C—CH₂ EtO₂C—CH₂ B-12 HOCH₂CH₂ HOCH₂CH₂ B-13EtOCH₂CH₂ EtOCH₂CH₂ B-14

B-15 CH₃ PhCH₂ B-16 CH₃COCH₂ CH₃COCH₂ B-17

B-18 CF₃CH₂ CF₃CH₂ B-19 Ph Ph B-20

B-21

B-22

B-23

B-24

B-25

B-26

B-27

B-28

B-29

B-30

B-31

B-32

B-33

B-34

B-35

B-36

B-37

B-38

B-39

B-40

B-41

B-42

B-43

B-44

B-45

B-46

B-47

B-48

B-49

B-50

No. R₁ B-51 iso-C₅H₁₁ B-52

B-53

B-54 PhCH₂CH₂ B-55

B-56

B-57

B-58

B-59

B-60 CH₂═CH—CH₂ B-61

B-62

B-63 Ph₃C B-64

B-65 CH≡C—CH₂ B-66 CH₃SO₂CH₂CH₂ B-67

B-68

No. R₁ R₂ B-69

B-70

B-71

B-72

B-73

B-74

B-75 iso-C₄H₉ PhCH₂

A further preferable example of the chemical species represented byFormula (II) is a combination, in which the chemical species [FL] is ananion represented by either one of Formula (II-5) and Formula (II-6)shown below, and the chemical species [Q] is the cation represented byFormula (II-4) shown above. The anion is represented by Formula (II-5)or (II-6) shown below.

wherein A¹, A², B¹, and B² each independently represent a substituent;L¹, L² , L³, L⁴, and L⁵ each represent a methine group; X¹ represents═O, ═NR, or ═C(CN), in which R represents a substituent; X² represents—O, —NR, or —C(CN)₂, in which R represents a substituent; m and n eachrepresent an integer of 0 to 2; Y¹ and E each represent an atom or anatom group necessary for forming a carbocyclic ring or a heterocyclicring; Z¹ and G each represent an atom or an atom group necessary forforming a carbocyclic ring or a heterocyclic ring; x and y eachindependently represent 0 or 1; M^(k+) represents an onium ion; and krepresents the number of charges.

The anion represented by Formula (II-5) or (II-6) will be described indetail below.

In the formulae, examples of the substituents represented by A¹, A², B¹and B² include the following:

a substituted or unsubstituted straight-chain, branched or cyclic alkylgroup having from 1 to 18 carbon atoms (preferably from 1 to 8 carbonatoms) (such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,sec-butyl, t-butyl, cyclohexyl, methoxyethyl, ethoxycarbonylethyl,cyanoethyl, diethylaminoethyl, hydroxyethyl, chloroethyl, acetoxyethyland trifluoromethyl);

a substituted or unsubstituted aralkyl group having from 7 to 18 carbonatoms (preferably from 7 to 12 carbon atoms) (such as benzyl andcarboxybenzyl);

an alkenyl group having from 2 to 18 carbon atoms (preferably from 2 to8 carbon atoms) (such as vinyl);

an alkynyl group having from 2 to 18 carbon atoms (preferably from 2 to8 carbon atoms) (such as ethynyl);

a substituted or unsubstituted aryl group having from 6 to 18 carbonatoms (preferably from 6 to 10 carbon atoms) (such as phenyl,4-methylphenyl, 4-methoxyphenyl, 4-carboxyphenyl and3,5-dicarboxyphenyl);

a substituted or unsubstituted acyl group having from 2 to 18 carbonatoms (preferably from 2 to 8 carbon atoms) (such as acetyl, propyonyl,butanoyl and chloroacetyl);

a substituted or unsubstituted alkyl sulfonyl or aryl sulfonyl grouphaving from 1 to 18 carbon atoms (preferably from 1 to 8 carbon atoms)(such as methanesulfonyl and p-toluenesulfonyl);

an alkylsulfinyl group having from 1 to 18 carbon atoms (preferably from1 to 8 carbon atoms) (such as methanesulfinyl, ethanesulfinyl andoctanesulfinyl);

an alkoxycarbonyl group having from 2 to 18 carbon atoms (preferablyfrom 2 to 8 carbon atoms) (such as methoxycarbonyl and ethoxycarbonyl);

an aryloxycarbonyl group having from 7 to 18 carbon atoms (preferablyfrom 7 to 12 carbon atoms) (such as phenoxycarbonyl,4-methylphenoxycarbonyl and 4-methoxyphenylcarbonyl);

a substituted or unsubstituted alkoxy group having from 1 to 18 carbonatoms (preferably from 1 to 8 carbon atoms) (such as methoxy, ethoxy,n-butoxy and methoxyethoxy);

a substituted or unsubstituted aryloxy group having from 6 to 18 carbonatoms (preferably from 6 to 10 carbon atoms) (such as phenoxy and4-methoxyphenoxy);

an alkylthio group having from 1 to 18 carbon atoms (preferably from 1to 8 carbon atoms) (such as methylthio and ethylthio);

an arylthio group having from 6 to 10 carbon atoms (such as phenylthio);

a substituted or unsubstituted acyloxy group having from 2 to 18 carbonatoms (preferably from 2 to 8 carbon atoms) (such as acetoxy,ethylcarbonyloxy, cyclohexylcarbonyloxy, benzoyloxy andchloroacetyloxy);

a substituted or unsubstituted sulfonyloxy group having from 1 to 18carbon atoms (preferably from 1 to 8 carbon atoms) (such asmethanesulfonyloxy);

a substituted or unsubstituted carbamoyloxy group having from 2 to 18carbon atoms (preferably from 2 to 8 carbon atoms) (such asmethylcarbamoyloxy and diethylcarbamoyloxy);

a substituted or unsubstituted amino group having from 0 to 18 carbonatoms (preferably from 0 to 8 carbon atoms) (such as unsubstitutedamino, methylamino, dimethylamino, diethylamino, anilino,methoxyphenylamino, chlorophenylamino, morphorino, piperidino,pyrrolidino, pyridylamino, methoxycarbonylamino, n-butoxycarbonylamino,phenoxycarbonylamino, methylcarbamoylamino, phenylcarbamoylamino,ethylthiocarbamoylamino, methylsulfamoylamino, phenylsulfamoylamino,acetylamino, ethylcarbonylamino, ethylthiocarbonylamino,cyclohexylcarbonylamino, benzoylamino, chloroacetylamino,methanesulfonylamino and benzenesulfonylamino);

a substituted or unsubstituted carbamoyl group having from 1 to 18carbon atoms (preferably from 1 to 8 carbon atoms) (such asunsubstituted carbamoyl, methylcarbamoyl, ethylcarbamoyl,n-butylcarbamoyl, t-butylcarbamoyl, dimethylcarbamoyl,morphorinocarbamoyl and pyrrolidinocarbamoyl);

a substituted or unsubstituted sulfamoyl group having from 0 to 18carbon atoms (preferably from 0 to 8 carbon atoms) (suchasunsubstitutedsulfamoyl, methylsulfamoylandphenylsulfamoyl)

a halogen atom (such as fluorine, chlorine and bromine), a hydroxylgroup, a nitro group; a cyano group; a carboxyl group; and

a heterocyclic group (such as oxazole, benzoxazole, thiazole,benzothiazole, imidazole, benzoimidazole, indolenine, pyridine,sulfolane, furan, thiophene, pyrazole, pyrrole, chroman and coumarin).

The substituent represented by A¹ and A² preferably has a Hammett'ssubstituent constant (σp) of 0.2 or more. The Hammett's substituentconstant is described, for example, in Chem. Rev., vol. 91, p. 165(1991). Particularly preferred examples of the substituent include acyano group, a nitro group, an alkoxy carbonyl group, an acyl group, acarbamoyl group, a sulfamoyl group, an alkylsulfonyl group, and anarylsulfonyl group.

The substituent represented by B¹ and B² is preferably an alkyl group,an aryl group, an alkoxy group, and an amino group.

Because [—C(=L¹)−(E)_(x−)C(═X¹)—] (hereinafter referred to as W1 forconvenience) connected to Y¹ and [—C(-L⁵)=(G)_(y)=C(—X²⁻)—] (hereinafterreferred to as W2 for convenience) connected to Z¹ are in a conjugatedstate, it is considered that the carbon ring or the heterocyclic ringformed with Y¹ and W1, and the carbon ring or the heterocyclic ringformed with Z¹ and W2 are each one of the resonance structures.

The carbon ring or the heterocyclic ring formed with Y¹ and W1, and Z¹and W2 is preferably a four-membered to seven-membered ring, andparticularly preferably a five-membered ring or a six-membered ring.These rings may form a condensed ring with other four-membered toseven-membered rings. These rings may have a substituent. Examples ofthe substituent include those exemplified as the substituentsrepresented by A¹, A², B¹ and B². Preferred examples of the heteroatomforming the heterocyclic ring include B, N, O, S, Se, and Te. It isparticularly preferably N, O, and S.

Also, x and y each independently represent 0 or 1, and preferably bothof them are 0.

X¹ represents ═O, ═NR or ═C(CN)₂. X² represents —O, —NR or —C(CN)₂. Rrepresents a substituent. Examples of the substituent represented by Rinclude those exemplified above as the substituents represented by A¹,A², B¹ and B². R preferably represents an aryl group, and particularlypreferably phenyl.

In the invention, it is preferred that X¹ is ═O, and X² is —O.

Examples of the carbon ring formed with Y¹ and W1, and Z¹ and W2 includethe following, in which Ra and Rb each independently represent ahydrogen atom or a substituent:

Preferred carbon rings are carbon rings represented by A-1 and A-4.

Examples of the heterocyclic ring formed with Y¹ and W1, and Z¹ and W2include the following, in which Ra, Rb and Rc each independentlyrepresent a hydrogen atom or a substituent:

Preferred heterocyclic rings are heterocyclic rings represented by A-5,A-6 and A-7.

Examples of the substituents represented by Ra, Rb and Rc include thoseexemplified above as the substituents represented by A¹, A², B¹ and B².

Ra, Rb and Rc may be connected to each other to form a carbon ring or aheterocyclic ring.

The methine groups represented by L¹, L², L³, L⁴ and L⁵ are eachindependently a methine group, which may have a substituent. Examples ofthe substituent include, for example, those exemplified above as thesubstituents represented by A¹, A², B¹ and B². Preferred examples of thesubstituent include an alkyl group, an aralkyl group, an aryl group, analkoxy group, an aryloxy group, an alkylthio group, an arylthio group, ahalogen atom, an amino group, a carbamoyl group and a heterocyclicgroup. A plurality of the substituents may be connected to each other toform a five-membered to seven-membered ring (such as a cyclopentenering, a 1-dimethylaminocyclopentene ring, a 1-diphenylaminocyclopentenering, a cyclohexene ring, a 1-chlorocyclohexene ring, an isophoronering, a 1-morphorinocyclopentene ring and a cycloheptene ring).

Further, k represents the number necessary for neutralizing the changeof the counter cation.

In the invention, it is preferred that both m and n are 1; m is 0 and nis 2; or m is 2 and n is 0.

Examples of the anions represented by Formula (II-5) and Formula (II-6)will be described in detail below.

No. Ra Rb B-1  COOEt H B-2  CODEt CH₃ B-3  COOEt

B-4  COOEt —CH₂CH₂OH B-5  COOCH₃

B-6  COOEt

B-7  COOEt CONHC₄H₉(n) B-8  COOEt CONHPh B-9  CN

B-10 COCH₃

B-11 CF₃

B-12 CONHCH₃ CH₃ B-13 CONHCH₃

B-14 CONHC₄H₉(n)

B-15

B-16 CONHCH₃

No. Ra Rb L₃ B-17 CONHC₄H₉(n) CONHC₄H₉(n) CH B-18

H ″ B-19

CH₃ ″ B-20

″ B-21

″ B-22

″ B-23

″ B-24

″ B-25

C(CH₃) B-26

CONHC₄H₉(n) CH B-27

″ B-28 —COOEt CH₂Ph ″ B-29 —SO₂CH₃

″

No. Ra Rb L₃ m n B-30 CH₃SO₂NH—

CH 1 1 B-31 HO

C(CONH₂) 1 1 B-32 CH₃

C(Ph) 1 1 B-33 CH₃

C(CH₂Ph) 1 1 B-34 CH₃

1 1 B-35 EtO—

CH 1 1 B-36 —NHCOCH₃

CH 1 1 B-37 —NHCOPh

CH 1 1 B-33 —NHCOPh —CONHC₄H₉(n) CH 1 1 B-39 —NHCOPh —CONHPh CH 1 1 B-40—COOEt

CH 1 0 B-41 —CN

CH 1 0 B-42 —CF₃

CH 1 0 B-43 —CONHC₄H₉(n)

CH 1 0 B-44 —NHCOC₄H₉(n)

CH 1 0

No. Ra Rb L₃ B-45

CH B-46 —NH₂

″ B-47 —NHCONHC₄H₉(n)

″ B-48 —NHCOOC₄H₉(n)

″ B-49

CH₂Ph ″ B-50

C(Ph) B-51

CH B-52

″ B-53 —CN

″ B-54 —CF₃

″

No. Ra Rb L B-55 —COOEt

C(CH₃) B-56 —CN

″ B-57 —CF₃

″ B-58 —COCH₃

″ B-59 —COOEt

″ B-60 —CN

″ B-61 —COOEt

C(Br) B-62 —COOEt

C(Cl) B-63 —CN

C(Br)

No. Ra Rb L B-64 —CN

C(Br) B-65 —COOEt

C(Cl) B-66 —COOEt

CH B-67 —CONHCH₃

CH B-68 —NHCOCH₃

CH B-69 —CH₃

CH B-70 —NH₂

CH

No. Ra Rb X L B-71 H H O CH B-72 H CH₃ O ″ B-73 H nC₄H₉ O ″ B-74 nC₄H₉nC₄H₉ O ″ B-75 H Ph O ″ B-76 H Ph O C(Ph) B-77 Ph Ph O CH B-78 H

O ″ B-79 H

O ″ B-80 H H S ″ B-81 H C₂H₅ S ″ B-82 C₂H₅ C₂H₅ S ″ B-83 H nC₄H₉ OC(CH₂Ph) B-84 H Ph O C(CH₃) B-85 H Ph S CH

No. Ra Rb X L B-86 H nC₄H₉ O CH B-87 H Ph O ″ B-88 CH₃ CH₃ O ″ B-89 PhPh O ″ B-90 H Ph O C(CH₃) B-91 H

O C(CH₂Ph) B-92 H nC₄H₉ S CH B-93 H Ph S ″ B-94 Ph Ph S ″ B-95 Et Et S ″B-96 H Ph S C(CH₃) B-97

B-98

B-99

B-100

B-101

B-102

B-103

B-104

B-105

B-106

B-107

B-108

B-109

B-110

B-111

B-112

B-113

B-114

B-115

B-116

B-117

B-118

B-119

B-120

B-121

B-122

B-123

B-124

B-125

B-126

B-127

B-128

B-129

B-130

B-131

B-132

B-133

B-134

B-135

B-136

B-137

B-138

B-139

B-140

B-141

B-142

B-143

B-144

B-145

B-146

B-147

B-148

B-149

B-150

B-151

B-152

B-153

B-154

B-155

B-156

B-157

B-158

B-159

B-160

B-161

FIGS. 1A, 1B, and 1C are schematic side views showing an embodiment ofthe recording medium in accordance with the present invention. Asillustrated in FIG. 1A, a recording medium 10 comprises a transparentsubstrate 11 and a recording layer 12 overlaid on the substrate 11.

The recording layer 12 is formed from a material, which is originallynot a fluorescent material and which has the properties such that, whenrecording light having a predetermined wavelength λ1 is irradiated tothe material, the material is capable of being caused to change into afluorescent material. By way of example, in this embodiment of therecording medium in accordance with the present invention, the recordinglayer 12 is formed from a material comprising a combination of thecompound represented by the formula shown below, which is one of thecompounds represented by Formula (II-1) shown above and acting as thechemical species [FL] capable of producing the fluorescence:

R¹ R² R³ M n-C₄H₉ CH₃ CH₃ I⁺and the compound A-1, which is one of the compounds represented byFormula (II-2) shown above and acting as the chemical species [Q]capable of quenching the fluorescence.

The material constituting the recording layer 12 has the properties suchthat, when the recording light having the predetermined wavelength λ1 isirradiated to the material, the material is capable of being caused tochange into the fluorescent material and such that, when excitationlight having a predetermined wavelength λ2 is then irradiated to thethus formed fluorescent material, the fluorescent material is capable ofbeing caused to produce fluorescence having a wavelength λ3. FIGS. 1A,1B, and 1C show the properties of the material constituting therecording layer 12. Specifically, as illustrated in FIG. 1A, even ifexcitation light 2 having the wavelength λ2 is irradiated to thematerial, while the material is being in its original state, thematerial does not produce the fluorescence. However, as illustrated inFIG. 1B, when recording light 1 having the wavelength λ1 is irradiatedto the material, the material, which is located at a site P having beenexposed to the recording light 1, is caused to change into thefluorescent material. Also, as illustrated in FIG. 1C, when theexcitation light 2 having the wavelength λ2 is then irradiated to thesite P, the fluorescent material having been formed at the site P iscaused to produce fluorescence 3 having the wavelength λ3.

As described above, in this embodiment of the recording medium inaccordance with the present invention, the recording layer 12 is formedfrom the material comprising the combination of the compound representedby the formula shown above, which is one of the compounds represented byFormula (II-1) shown above and acting as the chemical species [FL]capable of producing the fluorescence, and the compound A-1, which isone of the compounds represented by Formula (II-2) shown above andacting as the chemical species [Q] capable of quenching thefluorescence. In such cases, λ1=λ2≠λ3.

Embodiments of the information recording and reproducing apparatuses inaccordance with the present invention, in which the recording medium 10is employed, will be described hereinbelow.

FIG. 2 is a side view showing a first embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention. With reference to FIG. 2, the information recording andreproducing apparatus comprises a recording light source 13 forproducing the recording light 1 having the wavelength λ1 of 532 nm. Theinformation recording and reproducing apparatus also comprises a lens 14for diverging the recording light 1, and a collimator lens 15 forcollimating the recording light 1, which has been radiated out in thestate of divergent light from the lens 14. The information recording andreproducing apparatus further comprises a converging lens 16 forconverging the recording light 1, which has been collimated by thecollimator lens 15, onto the recording layer 12 of the recording medium10. The information recording and reproducing apparatus still furthercomprises an objective lens 17 for converging the fluorescence 3, whichhas been produced from the recording layer 12 in the manner describedlater. The information recording and reproducing apparatus alsocomprises a filter 18 for transmitting only the light having wavelengthsfalling within the wavelength region of the fluorescence 3, and aconverging lens 19 for converging the fluorescence 3, which has passedthrough the filter 18. The information recording and reproducingapparatus further comprises a photodetector 20 for detecting thefluorescence 3, which has been converged by the converging lens 19. Thephotodetector 20 may be constituted of, for example, photodiodes.

The recording layer 12 formed with the material comprising thecombination of the compounds described above has the properties suchthat, when the recording light 1 having the wavelength λ1 of 532 nm isirradiated to the recording layer 12, the material, which is located atthe site having been exposed to the recording light 1, changes into thefluorescent material and such that, when the excitation light 2 havingthe wavelength λ2 of 532 nm is then irradiated to the site, thefluorescent material having been formed at the site produces thefluorescence 3 having the wavelength λ3 of 650 nm.

By way of example, the recording light source 13 may be constituted of acombination of a semiconductor laser and an optical wavelengthconverting device. A modulation driving circuit 21 receives a digitalsignal S and drives the recording light source 13 in accordance with thedigital signal S. The photodetector 20 may be constituted of, forexample, photodiodes having sensitivity with respect to the wavelengthregion of the fluorescence 3.

How the first embodiment of the information recording and reproducingapparatus in accordance with the present invention operates will bedescribed hereinbelow.

Firstly, how information is recorded on the recording medium 10 will bedescribed hereinbelow. The digital signal S, such as an image signal orcomputer data, is fed into the modulation driving circuit 21. Inaccordance with the digital signal S, the modulation driving circuit 21drives the recording light source 13 and performs on-off modulation ofthe recording light 1.

As described above with reference to FIG. 1B, when the recording light1, which has been converged by the converging lens 16 into a fine lightspot, is irradiated to the recording layer 12 of the recording medium10, the material constituting the recording layer 12, which material islocated at the site having been exposed to the recording light 1,changes into the fluorescent material, and a fine pit is thereby formedwith the fluorescent material in the recording layer 12.

When the pit is formed in the manner described above, the recordingmedium 10 is moved by a known linear movement mechanism (not shown) andin the direction indicated by the arrow X. Therefore, a plurality ofpits are formed so as to stand in a line on the recording medium10.After the pits standing in a line have been formed, the recordingmedium 10 may be moved in a direction approximately normal to thedirection indicated by the arrow X. In this manner, the pits are capableof being formed such that the pits are arrayed in two-dimensionaldirections in the plane of the recording layer 12.

How the information, which has been recorded in the form of the pit onthe recording medium 10, is reproduced will be described hereinbelow.When the information is to be reproduced from the recording medium 10,the recording medium 10 is linearly moved in the same manner as that inthe recording of the information, and the recording light source 13 isdriven. At this time, the recording light source 13 is driven so as toproduce the light 2 having a predetermined intensity, which is lowerthan the intensity of the recording light 1, such that the materialconstituting the recording layer 12 may not be markedly caused by thelight 2 to change into the fluorescent material. In this embodiment, thelight 2 has the wavelength λ2 of 532 nm, which is identical with thewavelength λ1 of the recording light 1. The light 2 employed for thereproduction of the information is herein referred to as the excitationlight 2.

As described above, when the excitation light 2 is irradiated to therecording layer 12 of the recording medium 10, the fluorescence 3 havingthe wavelength λ3 of 650 nm is produced from the site at which the pithas been formed, i.e. the site at which the fluorescent material hasbeen formed. However, the fluorescence 3 is not produced from a site atwhich no pit has been formed.

The fluorescence 3 is detected by the photodetector 20 via the filter18. A fluorescence detection signal SR in accordance with the intensityof the fluorescence 3 is obtained from the photodetector 20. Therefore,by way of example, the fluorescence detection signal SR having beenobtained as a time-series signal may be sampled and quantized by beingsynchronized with the movement of the recording medium 10. In thismanner, the digital signal S is capable of being reproduced from therecording medium 10.

The excitation light 2 having the wavelength of 532 nm is filtered outby the filter 18 and is therefore not detected by the photodetector 20.In lieu of the optical filter 18, a prism, a grating, a holographicelement, or the like, may be employed as the wavelength selecting means.

As will be understood from the foregoing, in this embodiment, therecording light source 13 also acts as the source of the excitationlight for the reproduction of the information.

A second embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedherein below with reference to FIG. 3. In FIG 3 (and those that follow),similar elements are numbered with the same reference numerals withrespect to FIG. 2.

The second embodiment of the information recording and reproducingapparatus in accordance with the present invention, which is shown inFIG. 3, is constituted basically in the same manner as that in the firstembodiment of the information recording and reproducing apparatus shownin FIG. 2, except that a disk-like recording medium 30 is employed inlieu of the recording medium 10. The disk-like recording medium 30comprises the substrate and the recording layer, which are of the sametypes as those in the recording medium 10. In the second embodiment, thedirection of the optical path of each of the recording light 1 and theexcitation light 2 is changed by a mirror 31 toward the lens 14.

When the information is to be recorded and reproduced, the recordingmedium 30 is rotated by driving means (not shown) and in the directionindicated by the arrow R. Also, the entire optical system is moved withrespect to the recording medium 30 and in the radial direction of therecording medium 30. In this manner, the recording light 1 or theexcitation light 2 scans the recording medium 30 in two-dimensionaldirections and along a spiral path or concentric circular paths. Inorder to track the pits arrayed along the spiral line or concentriccircular lines, conventional tracking techniques for optical disks maybe utilized. The other operations for the information recording and theinformation reproduction are performed in the same manner as that in thefirst embodiment of FIG. 2.

A third embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 4. The third embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention, which is shown in FIG. 4, is constituted basically inthe same manner as that in the first embodiment of the informationrecording and reproducing apparatus shown in FIG. 2, except that a nearfield light head 40 is employed in lieu of the collimator lens 15 andthe converging lens 16.

The near field light head 40 has a micro-aperture 41 at a bottom end.The micro-aperture 41 has a diameter (of, by way of example,approximately several nanometers) shorter than the wavelength of therecording light 1. The micro-aperture 41 can be formed by, for example,pointing a bottom end portion of a core of an optical fiber, forming anopaque metal film 42 on the core of the optical fiber with a vacuumevaporation process, and thereafter removing the metal film 42 from onlythe bottom end of the core of the optical fiber.

When the recording light 1 is introduced into the near field light head40, evanescent wave E is radiated out from the micro-aperture 41 formedat the bottom end of the near field light head 40. When the evanescentwave E is irradiated to the recording layer 12 of the recording medium10, the material constituting the recording layer 12, which material islocated at the site having been exposed to the evanescent wave E,changes into the fluorescent material, and a fine pit is thereby formedwith the fluorescent material in the recording layer 12.Since theevanescent wave E is radiated out from the range of a diameter shorterthan the wavelength of the recording light 1, the diameter of the pit isshorter than the wavelength of the recording light 1. Therefore, therecording density is capable of being enhanced markedly.

Reproduction of the information from the recording medium 10 isperformed in the same manner as that in the first embodiment of FIG. 2.In such cases, the evanescent wave E acting as the excitation light,which is irradiated from the near field light head 40 to the recordinglayer 12, is radiated out from the range of a diameter shorter than thewavelength of the excitation light 2, which is introduced into the nearfield light head 40. Therefore, the evanescent wave E is capable ofbeing irradiated independently to each of the pits, which have beenformed in the recording layer 12 and which have a diameter shorter thanthe wavelength of the recording light 1.

FIG. 5 shows an image of a pit having been formed on the recordingmedium 10 with the third embodiment of FIG. 4, which image has beendetected with a near field optical microscope. As illustrated in FIG. 5,it has been confirmed that a pit having a diameter shorter than thewavelength λ1 (=532 nm) of the recording light 1 has been formed on therecording medium 10.

A fourth embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 6. The fourth embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention, which is shown in FIG. 6, is constituted basically inthe same manner as that in the first embodiment of the informationrecording and reproducing apparatus shown in FIG. 2, except that a solidimmersion lens 50 is located between the converging lens 16 and therecording medium 10. In cases where the solid immersion lens 50 isutilized in air, the solid immersion lens 50 has the characteristicssuch that, when light is entered from one end side of the solidimmersion lens 50 into the solid immersion lens 50, the solid immersionlens 50 radiates out the evanescent wave E from the other end (i.e., thebottom end in FIG. 6).

In cases where the solid immersion lens 50 is employed, as in caseswhere the near field light head 40 is employed in the third embodimentof FIG. 4, the diameter of the formed pit becomes shorter than thewavelength of the recording light 1, and therefore the recording densityis capable of being enhanced markedly.

A fifth embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 7. The fifth embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention, which is shown in FIG. 7, is constituted basically inthe same manner as that in the first embodiment of the informationrecording and reproducing apparatus shown in FIG. 2, except that,besides the recording light source 13, an excitation light source 60 isemployed for the reproduction of the information. Also, the excitationlight 2, which has been produced by the excitation light source 60, isreflected by a beam splitter 61, which has been inserted into theoptical path of the recording light 1. The excitation light 2, which hasbeen reflected by the beam splitter 61, follows the same optical path asthat of the recording light 1.

In the fifth embodiment of FIG. 7, as the recording light source 13, alight source producing the recording light 1 having the wavelength λ1 of350 nm is employed. Also, as the excitation light source 60, alightsource producing the excitation light 2 having the wavelength λ2 of 532nm is employed. Further, as a recording medium 10′, a recording mediumcomprising a recording layer 12′ formed from a specific material isemployed. The material constituting the recording layer 12′ has theproperties such that, when the recording light 1 having the wavelengthλ1 of 350 nm is irradiated to the material, the material is capable ofbeing caused to change into a fluorescent material and such that, whenthe excitation light 2 having the wavelength λ2 of 532 nm is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce the fluorescence 3 havingthe wavelength λ3 of 600 nm. As the material constituting the recordinglayer 12′, for example, the compound represented by Formula (I-4), whichis one of the compounds represented by Formula (I) shown above, may beemployed

In the fifth embodiment of FIG. 7, the recording of the information onthe recording medium 10′ is performed in the same manner as that in thefirst embodiment of FIG. 2. Also, the reproduction of the informationfrom the recording medium 10′ is performed by irradiating the excitationlight 2, which has been produced by the excitation light source 60 andwhich has a predetermined intensity, to the recording layer 12′ of therecording medium 10′. In such cases, even if the material constitutingthe recording layer 12′ is exposed to the excitation light 2 having thewavelength λ2 of 532 nm, the material will not change into thefluorescent material. Therefore, when the information is to bereproduced from the recording medium 10′, the intensity of theexcitation light 2 need not particularly be set at a low intensity.

A sixth embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 8. The sixth embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention, which is shown in FIG. 8, is constituted basically inthe same manner as that in the second embodiment of the informationrecording and reproducing apparatus shown in FIG. 3, except that,besides the recording light source 13, the excitation light source 60 isemployed for the reproduction of the information. Also, the excitationlight 2, which has been produced by the excitation light source 60, isreflected by the beam splitter 61, which has been inserted into theoptical path of the recording light 1. The excitation light 2, which hasbeen reflected by the beam splitter 61, follows the same optical path asthat of the recording light 1.

In the sixth embodiment of FIG. 8, the recording light source 13 and theexcitation light source 60, which are of the same types as those in thefifth embodiment of FIG. 7, are employed. Also, as a recording medium30′, a recording medium comprising a recording layer, which is of thesame type as the recording layer 12′ of the recording medium 10′employed in the fifth embodiment of FIG. 7, is employed. Therefore, inthe sixth embodiment of FIG. 8, the recording of the information and thereproduction of the information are performed in the same manner as thatin the fifth embodiment of FIG. 7 by driving the recording light source13 and the excitation light source 60 respectively.

A seventh embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 9. The seventh embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention, which is shown in FIG. 9, is constituted basically inthe same manner as that in the third embodiment of the informationrecording and reproducing apparatus shown in FIG. 4, except that,besides the recording light source 13, the excitation light source 60 isemployed for the reproduction of the information. Also, the excitationlight 2, which has been produced by the excitation light source 60, isreflected by the beam splitter 61, which has been inserted into theoptical path of the recording light 1. The excitation light 2, which hasbeen reflected by the beam splitter 61, follows the same optical path asthat of the recording light 1.

In the seventh embodiment of FIG. 9, the recording light source 13 andthe excitation light source 60, which are of the same types as those inthe fifth embodiment of FIG. 7, are employed. Also, as a recordingmedium 10′, a recording medium, which is of the same type as therecording medium 10′ employed in the fifth embodiment of FIG. 7, isemployed. Therefore, in the seventh embodiment of FIG. 9, the recordingof the information and the reproduction of the information are performedin the same manner as that in the fifth embodiment of FIG. 7 by drivingthe recording light source 13 and the excitation light source 60respectively.

An eighth embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 10. The eighth embodiment of theinformation recording and reproducing apparatus in accordance with thepresent invention, which is shown in FIG. 10, is constituted basicallyin the same manner as that in the fourth embodiment of the informationrecording and reproducing apparatus shown in FIG. 6, except that,besides the recording light source 13, the excitation light source 60 isemployed for the reproduction of the information. Also, the excitationlight 2, which has been produced by the excitation light source 60, isreflected by the beam splitter 61, which has been inserted into theoptical path of the recording light 1. The excitation light 2, which hasbeen reflected by the beam splitter 61, follows the same optical path asthat of the recording light 1.

In the eighth embodiment of FIG. 10, the recording light source 13 andthe excitation light source 60, which are of the same types as those inthe fifth embodiment of FIG. 7, are employed. Also, as a recordingmedium 10′, a recording medium, which is of the same type as therecording medium 10′ employed in the fifth embodiment of FIG. 7, isemployed. Therefore, in the eighth embodiment of FIG. 10, the recordingof the information and the reproduction of the information are performedin the same manner as that in the fifth embodiment of FIG. 7 by drivingthe recording light source 13 and the excitation light source 60respectively.

In the recording medium in accordance with the present invention, thematerial employed for forming the recording layer is not limited to thematerials, which are employed in the recording media 10, 10′, 30, and30′ described above.

For example, the recording layer may be formed from a materialcomprising a combination of the compound B-6, which is one of thecompounds represented by Formula (II-1) shown above and acting as thechemical species [FL] capable of producing the fluorescence, and thecompound A-4, which is one of the compounds represented by Formula(II-2) shown above and acting as the chemical species [Q] capable ofquenching the fluorescence. The material has the properties such that,when the recording light having the wavelength of 532 nm is irradiatedto the material, the material is capable of being caused to change intothe fluorescent material and such that, when the excitation light havingthe wavelength of 532 nm is then irradiated to the thus formedfluorescent material, the fluorescent material is capable of beingcaused to produce the fluorescence.

Alternatively, the recording layer may be formed from a materialcomprising a combination of the compound A-11, which is one of thecompounds represented by Formula (II-3) shown above and acting as thechemical species [FL] capable of producing the fluorescence, and thecompound B-40, which is one of the compounds represented by Formula(II-4) shown above and acting as the chemical species [Q] capable ofquenching the fluorescence. The material has the properties such that,when the recording light having the wavelength of 680 nm is irradiatedto the material, the material is capable of being caused to change intothe fluorescent material and such that, when the excitation light havingthe wavelength of 680 nm is then irradiated to the thus formedfluorescent material, the fluorescent material is capable of beingcaused to produce the fluorescence having the wavelength of 750 nm.

As another alternative, the recording layer may be formed from amaterial comprising a combination of the compound B-74, which is one ofthe compounds represented by Formula (II-5) shown above and acting asthe chemical species [FL] capable of producing the fluorescence, and thecompound B-5, which is one of the compounds represented by Formula(II-4) shown above and acting as the chemical species [Q] capable ofquenching the fluorescence. The material has the properties such that,when the recording light having the wavelength of 680 nm is irradiatedto the material, the material is capable of being caused to change intothe fluorescent material and such that, when the excitation light havingthe wavelength of 680 nm is then irradiated to the thus formedfluorescent material, the fluorescent material is capable of beingcaused to produce the fluorescence.

As a further alternative, the recording layer may be formed from amaterial comprising a combination of the compound B-136, which is one ofthe compounds represented by Formula (II-6) shown above and acting asthe chemical species [FL] capable of producing the fluorescence, and thecompound B-64, which is one of the compounds represented by Formula(II-4) shown above and acting as the chemical species [Q] capable ofquenching the fluorescence. The material has the properties such that,when the recording light having the wavelength of 532 nm is irradiatedto the material, the material is capable of being caused to change intothe fluorescent material and such that, when the excitation light havingthe wavelength of 532 nm is then irradiated to the thus formedfluorescent material, the fluorescent material is capable of beingcaused to produce the fluorescence.

The material, which is employed for forming the recording layer of eachof the recording media 10, 10′, 30, and 30′ in the first to eighthembodiments described above, has the characteristics such that, when therecording light 1 having the wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into thefluorescent material and such that, when the excitation light 2 havingthe wavelength λ2 and having a predetermined intensity is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce the fluorescence 3 havingan intensity in accordance with the intensity of the recording light 1.FIG. 11 shows the characteristics of the material.

Therefore, each of the first to eighth embodiments described above iscapable of being constituted as a multi-valued information recording andreproducing apparatus. In such cases, as the digital signal S fed intothe modulation driving circuit 21, a signal carrying multi-valuedinformation, such as a gradation image signal, is employed. When themulti-valued information is to be recorded on the recording medium, asin each of the embodiments described above, the digital signal S, suchas an image signal or computer data, is fed into the modulation drivingcircuit 21. In accordance with the digital signal S, the modulationdriving circuit 21 drives the recording light source 13 and modulatesthe recording light 1. Specifically, the modulation driving circuit 21drives and recording light source 13 and modulates the recording light 1such that, in cases where the signal value of the digital signal S islarge, the intensity of the recording light 1 becomes high. In thismanner, the multi-valued information is recorded in the form of the pitson each of the recording media 10, 10′, 30, and 30′.

When the multi-valued information, which has been recorded in the formof the pits on each of the recording media 10, 10′, 30, and 30′, is tobe reproduced, the excitation light 2 having the predetermined intensityis irradiated to the recording layer of the recording medium in the samemanner as that in each of the first to eighth embodiments describedabove.

As described above, when the excitation light 2 is irradiated to therecording layer of the recording medium, on which the multi-valuedinformation has been recorded, the fluorescence 3 is produced from thesite at which the pit has been formed, i.e. the site at which thefluorescent material has been formed. However, the fluorescence 3 is notproduced from a site at which no pit has been formed. Also, since therecording layer is formed from the material having the characteristicsdescribed above, the fluorescence 3 having a high intensity is producedfrom a pit, which was exposed to the recording light 1 having a highintensity.

The fluorescence 3 is detected by the photodetector 20 via the filter18. The fluorescence detection signal SR in accordance with theintensity of the fluorescence 3 is obtained from the photodetector 20.Therefore, by way of example, the fluorescence detection signal SRhaving been obtained as a time-series signal may be sampled andquantized by being synchronized with the movement of the recordingmedium in this manner, the digital signal S carrying the multi-valuedinformation is capable of being reproduced from the recording medium 10.

As described above, the fluorescence 3 having a high intensity isproduced from a pit, which was exposed to the recording light 1 having ahigh intensity. Therefore, the intensity of the fluorescence detectionsignal SR with respect to the pit becomes high. Accordingly, inaccordance with the intensity of the fluorescence detection signal SR,the multi-valued information represented by the digital signal S iscapable of being reproduced. FIG. 12 shows an example of thedistribution of the intensities of the fluorescence detection signal SR(i.e., the reproduced signal), which distribution is obtained in caseswhere the digital signal S is a ten-valued signal.

FIG. 13 is a side view showing a ninth embodiment of the informationrecording and reproducing apparatus in accordance with the presentinvention. With reference to FIG. 13, the information recording andreproducing apparatus comprises a recording control section 110, andthree laser driving circuits 111 a, 111 b, and 111 c, which arecontrolled by the recording control section 110. The informationrecording and reproducing apparatus also comprises recording lasers 112a, 112 b, and 112 c, which may be constituted of semiconductor lasers,and the like, and which are driven respectively by the laser drivingcircuits 111 a, 111 b, and 111 c. The information recording andreproducing apparatus further comprises a mirror 115 a for reflectingrecording light (in this case, a recording laser beam) 113 a, which hasbeen produced by the recording laser 112 a, toward an optical fiber 114.The information recording and reproducing apparatus still furthercomprises dichroic mirrors 115 b and 115 c for respectively reflectingrecording light (in this case, a recording laser beam) 113 b andrecording light (a recording laser beam) 113 c, which have been producedrespectively by the recording lasers 112 b and 112 c, toward the opticalfiber 114.

One end side of the optical fiber 114 has been processed to form amicro-aperture probe 114 a, which will be described later. The recordinglasers 112 a, 112 b, and 112 c respectively produce the recording laserbeams 113 a, 113 b, and 113 c, which respectively have differentwavelengths λ1 a, λ1 b, and λ1 c. In this embodiment, λ1 a=488 nm, λ1b=640 nm, and λ1 c=780 nm. The dichroic mirror 115 b transmits therecording laser beam 113 a having the wavelength λ1 a. The dichroicmirror 115 c transmits the recording laser beam 113 a having thewavelength λ1 a and the recording laser beam 113 b having the wavelengthλ1 b. In this manner, the recording laser beams 113 a, 113 b, and 113 care combined with one another, and the combined recording laser beamsimpinge upon the other end 114 b of the optical fiber 114 and enter intothe optical fiber 114.

The information recording and reproducing apparatus also comprises anexcitation control section 130, and three laser driving circuits 131 a,131 b, and 131 c, which are controlled by the excitation control section130. The information recording and reproducing apparatus furthercomprises excitation lasers 132 a, 132 b, and 132 c, which may beconstituted of semiconductor lasers, and the like, and which are drivenrespectively by the laser driving circuits 131 a, 131 b, and 131 c. Theinformation recording and reproducing apparatus still further comprisesdichroic mirrors 135 a, 135 b and 135 c for respectively reflectingexcitation light (in this case, an excitation laser beam) 133 a,excitation light (an excitation laser beam) 133 b, and excitation light(an excitation laser beam) 133 c, which have been produced respectivelyby the excitation lasers 132 a, 132 b, and 132 c, toward the opticalfiber 114.

The excitation lasers 132 a, 132 b, and 132 c respectively produce theexcitation laser beams 133 a, 133 b, and 133 c, which respectively havedifferent wavelengths λ2 a, λ2 b, and λ2 c. In this embodiment, λ2 a=488nm, λ2 b=640 nm, and λ2 c=780 nm. The dichroic mirrors 135 a, 135 b and135 c are located in the optical path of the recording laser beams 113a, 113 b, and 113 c, which have been combined with one another in themanner described above. The dichroic mirrors 135 a, 135 b and 135 ctransmit all of the combined recording laser beams 113 a, 113 b, and 113c. The dichroic mirror 135 b also transmits the excitation laser beam133 a having the wavelength λ2 a. The dichroic mirror 135c alsotransmits the excitation laser beam 133 a having the wavelength λ2 a andthe excitation laser beam 133 b having the wavelength λ2 b. In thismanner, the excitation laser beams 133 a, 133 b, and 133 c are combinedwith one another, and the combined excitation laser beams impinge uponthe other end 114 b of the optical fiber 114 and enter into the opticalfiber 114.

The recording control section 110 and the excitation control section 130are controlled by a controller (a general control section) 124.

A piezo-electric device 120 is located at the micro-aperture probe 114a. Also, a disk-like recording medium 122 is supported on a turn table121 and is located at a position in the vicinity of the bottom end ofthe micro-aperture probe 114 a. The turn table 121 rotates the recordingmedium 122. The turn table 121 can also be moved in three-dimensionaldirections X, Y, and Z by turn table driving means 123, which may beconstituted of a piezo-electric device, or the like. The turn tabledriving means 123 is controlled by the controller 124.

The information recording and reproducing apparatus also comprises alaser 126 for producing a laser beam 125, which is utilized forcontrolling the position of the turn table 121 with respect to thedirection Z. The information recording and reproducing apparatus furthercomprises a converging lens 127 for converging the laser beam 125 toform a laser beam spot at the bottom end of the micro-aperture probe 114a, a converging lens 128 for converging the laser beam 125, which hasdiverged after being converged by the converging lens 127, and aphotodetector 129 for detecting the laser beam 125, which has beenconverged by the converging lens 128 The output of the photodetector 129is fed into the controller 124.

Furthermore, three photodetectors 140 a, 140 b, and 140 c are located ata position in the vicinity of the micro-aperture probe 114 a. Thephotodetectors 140 a, 140 b, and 140 c respectively detect fluorescencehaving a wavelength λ3 a of 540 nm, fluorescence having a wavelength λ3b of 750 nm, and fluorescence having a wavelength λ3 c of 850 nm, whichare produced from the recording medium 122 in the manner describedlater. The outputs of the photodetectors 140 a, 140 b, and 140 c arerespectively amplified by amplifiers 141 a, 141 b, and 141 c. Theoutputs having been amplified are fed into a read-out processing section142. The read-out processing section 142 is controlled by the controller124.

The micro-aperture probe 114 a has a micro-aperture at the bottom end.The micro-aperture has a diameter (of, by way of example, approximatelyseveral nanometers) shorter than the wavelengths λ1 a, λ1 b, and λ1 c.By way of example, as illustrated in detail in FIG. 14, themicro-aperture can be formed by pointing a bottom end portion of a core114 c of the optical fiber 114, forming an opaque metal film 114 d onthe core 114 c of the optical fiber 114 with a vacuum evaporationprocess, and thereafter removing the metal film 114 d from only thebottom end of the core 114 c of the optical fiber 114.

Also, as illustrated in FIG. 14, the recording medium 122 comprises asubstrate 122 a and a recording layer 122 b overlaid on the substrate122 a. By way of example, the recording layer 122 b is constituted of athin film containing three kinds of materials A, B, and C, which areuniformly mixed with one another.

The material A has the properties such that, when the recording laserbeam 113 a having the wavelength λ1 a of 488 nm is irradiated to thematerial, the material is capable of being caused to change into thefluorescent material and such that, when the excitation laser beam 133 ahaving the wavelength λ2 a of 488 nm is then irradiated to the thusformed fluorescent material, the fluorescent material is capable ofbeing caused to produce the fluorescence having the wavelength λ3 a inthe vicinity of 540 nm. By way of example, the material A may comprise acombination of the anion A-2, which is one of the anions represented byFormula (II-3) shown above and acting as the chemical species [FL]capable of producing the fluorescence, and the cation B-40, which is oneof the cations represented by Formula (II-4) shown above and acting asthe chemical species [Q] capable of quenching the fluorescence.

The material B has the properties such that, when the recording laserbeam 113 b having the wavelength λ1 b of 640 nm is irradiated to thematerial, the material is capable of being caused to change into thefluorescent material and such that, when the excitation laser beam 133 bhaving the wavelength λ2 b of 640 nm is then irradiated to the thusformed fluorescent material, the fluorescent material is capable ofbeing caused to produce the fluorescence having the wavelength λ3 b inthe vicinity of 750 nm. By way of example, the material B may comprise acombination of the compound B-6, which is one of the compoundsrepresented by Formula (II-1) shown above and acting as the chemicalspecies [FL] capable of producing the fluorescence, and the compoundA-4, which is one of the cations represented by Formula (II-2) shownabove and acting as the chemical species [Q] capable of quenching thefluorescence.

The material C has the properties such that, when the recording laserbeam 113 c having the wavelength λ1 c of 780 nm is irradiated to thematerial, the material is capable of being caused to change into thefluorescent material and such that, when the excitation laser beam 133 chaving the wavelength λ2 c of 780 nm is then irradiated to the thusformed fluorescent material, the fluorescent material is capable ofbeing caused to produce the fluorescence having the wavelength λ3 c inthe vicinity of 850 nm. By way of example, the material C may comprise acombination of the anion B-76, which is one of the anions represented byFormula (II-5) shown above and acting as the chemical species [FL]capable of producing the fluorescence, and the cation B-5, which is oneof the cations represented by Formula (II-4) shown above and acting asthe chemical species [Q] capable of quenching the fluorescence.

How the ninth embodiment of the information recording and reproducingapparatus in accordance with the present invention operates will bedescribed hereinbelow.

Firstly, how the information is recorded on the recording medium 122will be described hereinbelow. The digital signal S, such as an imagesignal or computer data, is fed into the recording control section 110.The recording control section 110 separates the digital signal S intothree groups of equal signal lengths in accordance with a predeterminedformat. Specifically, for example, in cases where the digital signal Sis a 24-bit signal, processing is performed such that the digital signalS may be separated into signals of 8 bits+8 bits+8 bits The recordingcontrol section 110 controls the laser driving circuit 111 a inaccordance with a signal of a first group, which is among the signals ofthe three groups. Also, the recording control section 110 controls thelaser driving circuit 111 b in accordance with a signal of a secondgroup and controls the laser driving circuit 111 c in accordance with asignal of a third group. In this manner, the recording laser beams 113a, 113 b, and 113 c are respectively subjected to on-off modulation inaccordance with the signals of the first group, the second group, andthe third group.

As illustrated in FIG. 14, when the recording laser beam 113 a followsthe optical path described above and enters into the optical fiber 114,an evanescent wave E having the wavelength λ1 a is radiated out from themicro-aperture probe 114 a, which is formed at the bottom end of theoptical fiber 114. When the evanescent wave E is irradiated to therecording layer 122 b, the material A constituting the recording layer122 b, which material is located at the site having been exposed to theevanescent wave E, changes into a fluorescent material A, and a fine pitis thereby formed with the fluorescent material A in the recording layer122 b. In the same manner as that described above, when the recordinglaser beam 113 b enters into the optical fiber 114, an evanescent wave Ehaving the wavelength λ1 b is radiated out from the micro-aperture probe114 a, and the material B constituting the recording layer 122 b, whichmaterial is located at the site having been exposed to the evanescentwave E, changes into a fluorescent material B. As a result, a fine pitis formed with the fluorescent material B in the recording layer 122 b.Also, when the recording laser beam 113 c enters into the optical fiber114, an evanescent wave E having the wavelength λ1 c is radiated outfrom the micro-aperture probe 114 a, and the material C constituting therecording layer 122 b, which material is located at the site having beenexposed to the evanescent wave E, changes into a fluorescent material C.As a result, a fine pit is formed with the fluorescent material C in therecording layer 122 b.

In cases where the recording laser beams 113 a, 113 b, and 113 csimultaneously enter into the optical fiber 114, the three kinds of thepits described above are formed at an identical site on the recordinglayer 122 b, at which site the materials A, B, and C have been uniformlymixed with one another. Specifically, with this embodiment, basically, arecording density three times as high as the recording density, which isobtained when the information is recorded with one kind of recordinglight, is capable of being obtained.

Also, since each of the evanescent waves E, E, E described above isradiated out from the range of a diameter shorter than the wavelengthsof the recording laser beams 113 a, 113 b, and 113 c, the diameter ofthe pit is shorter than the wavelengths of the recording laser beams 113a, 113 b, and 113 c. Therefore, the recording density is capable ofbeing enhanced markedly.

When the pit described above is formed, the recording medium 122 isrotated by the turn table 121, and the micro-aperture probe 114 a ismoved by a known linear movement mechanism (not shown) and in the radialdirection of the recording medium 122. Therefore, each evanescent waveE, which is radiated out from the micro-aperture probe 114 a, scans therecording medium 122 along a spiral path or concentric circular paths.As a result, the pits arrayed along the spiral line or concentriccircular lines are formed on the recording medium 122.

In cases where the recording of the information is performed in themanner described above, it is necessary that the distance between thebottom end of the micro-aperture probe 114 a and the turn table 121 bekept at a predetermined length of distance. How the distance is kept atthe predetermined length of distance will be described hereinbelow.

Specifically, the bottom end portion of the micro-aperture probe 114 ais subjected to resonance vibration with the piezo-electric device 120described above, and the turn table 121 is moved vertically by the turntable driving means 123. In this manner, the distance between the bottomend of the micro-aperture probe 114 a and the surface of the recordingmedium 122 is altered. At this time, when the bottom end of themicro-aperture probe 114 a and the surface of the recording medium 122become close to each other, van der Waals force begins to act betweenthe bottom end of the micro-aperture probe 114 a and the surface of therecording medium 122. As a result, shear force acts on themicro-aperture probe 114 a, and an amplitude of vibration of themicro-aperture probe 114 a varies accompanying the shear force.Therefore, the laser beam 125 is converged at the bottom end of themicro-aperture probe 114 a, and diffracted light of the laser beam 125is detected by the photodetector 129. In this manner, the amplitude ofvibration of the micro-aperture probe 114 a is measured. The amplitudeof vibration depends upon the distance between the bottom end of themicro-aperture probe 114 a and the surface of the recording medium 122.Accordingly, the turn table driving means 123 is controlled by thecontroller 124 such that the amplitude of vibration may be kept at apredetermined value, and the distance between the bottom end of themicro-aperture probe 114 a and the surface of the recording medium 122is thereby kept at the predetermined length of distance.

How the information, which has been recorded in the form of the pit onthe recording medium 122, is reproduced from the recording medium 122will be described hereinbelow. When the reproduction of the informationis to be performed, the recording medium 122 is rotated by the turntable 121. Also, the excitation control section 130 controls the laserdriving circuits 131 a, 131 b, and 131 c such that the excitation lasers132 a, 132 b, and 132 c respectively produce the excitation laser beams133 a, 133 b, and 133 c having a predetermined intensity. When theexcitation laser beams 133 a, 133 b, and 133 c follow the optical pathdescribed above and enter into the optical fiber 114, evanescent wavesE, E, E respectively having the wavelengths λ2 a, λ2 b, and λ2 c areradiated out from the micro-aperture probe 114 a and are irradiated tothe recording layer 122 b of the recording medium 122.

When the evanescent wave E having the wavelength λ2 a is irradiated tothe site (the pit) on the recording layer 122 b, at which site thematerial A has changed into the fluorescent material A, the fluorescentmaterial A is excited to produce the fluorescence having the wavelengthλ3 a. Even if the evanescent wave E having the wavelength λ2 a isirradiated to a site on the recording layer 122 b, at which site thematerial A has not changed into the fluorescent material A, nofluorescence will be produced from the site. Also, when the evanescentwave E having the wavelength λ2 b is irradiated to the site (the pit) onthe recording layer 122 b, at which site the material B has changed intothe fluorescent material B, the fluorescent material B is excited toproduce the fluorescence having the wavelength λ3 b. Even if theevanescent wave E having the wavelength λ2 b is irradiated to a site onthe recording layer 122 b, at which site the material B has not changedinto the fluorescent material B, no fluorescence will be produced fromthe site. Further, when the evanescent wave E having the wavelength λ2 cis irradiated to the site (the pit) on the recording layer 122 b, atwhich site the material C has changed into the fluorescent material C,the fluorescent material C is excited to produce the fluorescence havingthe wavelength λ3 c. Even if the evanescent wave E having the wavelengthλ2 c is irradiated to a site on the recording layer 122 b, at which sitethe material C has not changed into the fluorescent material C, nofluorescence will be produced from the site.

The photodetectors 140 a 140 b, and 140 c respectively have spectralsensitivity peaks at wavelengths in the vicinity of the wavelengths λ3a, λ3, and λ3 c of the fluorescence. Therefore, of the producedfluorescence, the fluorescence having the wavelength λ3 a is detectedindependently by the photodetector 140 a. Also, the fluorescence havingthe wavelength λ3 b is detected independently by the photodetector 140b, and the fluorescence having the wavelength λ3 c is detectedindependently by the photodetector 140 c. At this time, in order totrack the pits arrayed along the spiral line or concentric circularlines, the conventional tracking techniques for optical disks may beutilized.

Fluorescence detection signals, which have been obtained respectivelyfrom the photodetectors 140 a, 140 b, and 140 c, are respectivelyamplified by the amplifiers 141 a, 141 b, and 141 c. The amplifiedsignals are fed into the read-out processing section 142. The read-outprocessing section 142 forms signals of the first group, the secondgroup, and the third group described above respectively from the threeseries of the signals. Also, from the thus formed signals, the read-outprocessing section 142 reproduces the digital signal S before beingseparated into the three groups.

As described above, with the ninth embodiment of FIG. 13, the digitalsignal S is capable of being recorded at a markedly high density on therecording medium 122. Also, the recorded information is capable of beingreproduced from the recording medium 122.

In the ninth embodiment of FIG. 13, the digital signal S is separatedinto the three groups of equal signal lengths, the recording lasers 112a, 112 b, and 112 c are driven in parallel, and the signals of the threegroups are recorded in parallel. Alternatively, firstly, only therecording laser 112 a may be driven, and the signal may thereby berecorded on the entire area of the recording layer 122 b of therecording medium 122. Thereafter, only the recording laser 112 b may bedriven, and the signal may thereby be recorded on the entire area of therecording layer 122 b of the recording medium 122. Also, only therecording laser 112 c may then be driven, and the signal may thereby berecorded on the entire area of the recording layer 122 b of therecording medium 122.

A tenth embodiment of the information recording and reproducingapparatus in accordance with the present invention will be describedhereinbelow with reference to FIG. 15. In the tenth embodiment of FIG.15, in lieu of the micro-aperture probe 114 a described above, a solidimmersion lens 150 is employed. In cases where the solid immersion lens150 is utilized in air, the solid immersion lens 150 has thecharacteristics such that, when light is entered from one end side ofthe solid immersion lens 150 into the solid immersion lens 150, thesolid immersion lens 150 radiates out the evanescent wave E from theother end (i.e., the bottom end in FIG. 15).

The solid immersion lens 150 is capable of being utilized forirradiating the recording light to a recording layer 155 b of arecording medium 155 and for irradiating the excitation light to therecording layer 155 b. (In FIG. 15, reference numeral 155 a representsthe substrate of the recording medium 155.) In cases where thewavelength of the evanescent wave E radiated out from the solidimmersion lens 150 is represented by A, and the refractive index of themedium of the lens is represented by n, the diameter of the range, fromwhich the evanescent wave E is radiated out, is equal to A/n, which isshorter than the wavelength λ. Therefore, in cases where the recordingof the information is performed by the utilization of the solidimmersion lens 150, the diameter of the pit is capable of being keptshorter than the wavelength of the recording light, and the informationis capable of being recorded at a high density.

In cases where the solid immersion lens 150 is utilized, as the read-outmeans for detecting the fluorescence, the read-out means shown in FIG.13 may be utilized. Alternatively, the read-out means shown in FIG. 15may be utilized. By way of example, the read-out means shown in FIG. 15corresponds to the recording layer 155 b, which is constituted of onekind of material capable of changing into the fluorescent material. Theread-out means shown in FIG. 15 comprises a converging lens 152 forconverging fluorescence 151 having been produced from the recordinglayer 155 b. The read-out means shown in FIG. 15 also comprises a filter153 for transmitting light having wavelengths falling within thewavelength region of the fluorescence 151 and filtering out light havingwavelengths falling within the wavelength region of the evanescent waveE, which acts as the excitation light The read-out means shown in FIG.15 further comprises a photodetector 154 for detecting the fluorescence151 having passed through the filter 153.

In cases where the recording layer 155 b comprises multiple kinds ofmaterials, which have been uniformly mixed with one another, and theinformation having been recorded with multiple recording on therecording layer 155 b is to be readout, the read-out means describedabove may be utilized. Specifically in such cases, as the filter 153, afilter for filtering out light having wavelengths falling within thewavelength region of the evanescent wave E, which acts as the excitationlight, and transmitting light having wavelengths falling within thewavelength region of the fluorescence may be provided to correspond toeach of the excitation laser beams. Also, when the excitation laser beamis changed over to a different excitation laser beam, the filtercorresponding to the excitation laser beam may be selected and locatedin front of the photodetector 154.

In the aforesaid ninth embodiment of FIG. 13, the wavelength selectingmeans, such as the filter 153, should preferably be utilized whennecessary. Also, in lieu of the optical filter 153, a prism, a grating,a holographic element, or the like, may be employed as the wavelengthselecting means.

A different embodiment of the recording medium in accordance with thepresent invention and how the recording and the reproduction ofinformation are performed with respect to the different embodiment ofthe recording medium will be described hereinbelow with reference toFIG. 16. With reference to FIG. 16, a recording medium 160 comprises asubstrate 161, which is constituted of a dielectric block having aprism-like shape, a metal film 162 formed on one surface of thesubstrate 161, and a recording layer 163 overlaid on the metal film 162.

The metal film 162 should preferably be formed from, for example, goldor silver. The recording layer 163 comprises a material having theproperties such that, when the recording light is irradiated to thematerial, the material is capable of being caused to change into thefluorescent material. The recording layer 163 may comprise one kind ofthe material. Alternatively, such that multiple recording may beperformed, the recording layer 163 may comprise multiple kinds of thematerials, which have been uniformly mixed with one another. By way ofexample, the cases where the recording layer 163 comprises one kind ofthe material will be described hereinbelow.

When recording light 164 having the wavelength λ1, which recording lightcarries the recording information, is irradiated to the recording layer163, the material constituting the recording layer 163 changes into thefluorescent material. Therefore, in cases where the recording layer 163is two-dimensionally scanned with the recording light 164, the recordinginformation is capable of being recorded in the form of, for example,the pit described above on the recording layer 163.

After the recording information has been recorded on the recording layer163, excitation light 165 having the wavelength λ2 is irradiated fromthe side of the substrate 161 to the recording medium 160 such that theexcitation light 165 impinges at a specific angle of incidence upon aninterface between the substrate 161 and the metal film 162. As a result,surface plasmon resonance is excited at the metal film 162, and a plasmawave (a light wave) oozes out and impinges upon the recording layer 163.When the light having the wavelength λ2 is thus irradiated to therecording layer 163, fluorescence 166 having the wavelength λ3 isproduced from the fluorescent material having been formed in therecording layer 163. Accordingly, the interface between the substrate161 and the metal film 162 is two-dimensionally scanned with theexcitation light 165, and the fluorescence produced from the recordinglayer 163 is detected with respect to each of the positions which arebeing scanned with the excitation light 165. In this manner, therecording information is capable of being reproduced from the recordingmedium 160.

Alternatively, in lieu of the substrate 161 being constituted of thedielectric block having the prism-like shape, the substrate may beconstituted of a dielectric block having an approximately rectangularparallelepiped shape, and the substrate and an independent prism may becoupled with each other via a refractive index matching liquid. In suchcases, the substrate and the prism may be formed from an identicalmaterial, and a refractive index matching liquid having a refractiveindex identical with the refractive index of the substrate and the prismmaybe employed. In this manner, a structure optically equivalent to thestructure shown in FIG. 16 is capable of being obtained.

A further different embodiment of the recording medium in accordancewith the present invention and how the recording and the reproduction ofinformation are performed with respect to the further differentembodiment of the recording medium will be described hereinbelow withreference to FIG. 17. With reference to FIG. 17, a recording medium 170comprises a substrate 171, which is permeable to excitation lightdescribed later, and a recording layer 172 overlaid on one surface ofthe substrate 171.

The recording layer 172 comprises a material having the properties suchthat, when the recording light is irradiated to the material, thematerial is capable of being caused to change into the fluorescentmaterial. The recording layer 172 may comprise one kind of the material.Alternatively, such that multiple recording may be performed, therecording layer 172 may comprise multiple kinds of the materials, whichhave been uniformly mixed with one another. By way of example, the caseswhere the recording layer 172 comprises the three kinds of the materialsA, B, and C described above will be described hereinbelow.

When recording light beams 173 a, 173 b, and 173 c respectively havingthe wavelengths λ1 a, λ1 b, and λ1 c, which recording light beams carrythe recording information, are irradiated to the recording layer 172,the materials A, B, and C constituting the recording layer 172respectively change into the fluorescent materials A, B, and C.Therefore, in cases where the recording layer 172 is two-dimensionallyscanned with the recording light beams 173 a, 173 b, and 173 c, therecording information is capable of being recorded in the form of, forexample, the pit described above on the recording layer 172. By way ofexample, the recording layer 172 may be formed by overlaying a thinfilm, which contains the three kinds of the materials A, B, and Cuniformly mixed with one another, on the substrate 171.

After the recording information has been recorded on the recording layer172, excitation light 174 is entered from an end face of the substrate171 into the substrate 171 such that the excitation light 174 propagatesthrough repeated total reflection between the two surfaces of thesubstrate 171. As a result, an evanescent wave oozes out from thesubstrate 171 toward the recording layer 172 over the entire area of therecording layer 172. The evanescent wave is thus irradiated to therecording layer 172.

In such cases, as the excitation light 174, for example, white lightcontaining light having the wavelengths λ2 a, λ2 b, and λ2 c, whichrespectively fall within the excitation wavelength regions for thefluorescent materials A, B, and C, may be employed. Alternatively, asthe excitation light 174, a mixture of three-color light beamsrespectively having wavelengths, which primarily fall within thewavelength regions of λ2 a, λ2 b, and λ2 c, may be employed. As anotheralternative, three-color excitation light beams respectively havingwavelengths, which primarily fall within the wavelength regions of λ2 a,λ2 b, and λ2 c, may be irradiated to the recording layer 172independently and with different timings.

When the evanescent wave described above is irradiated to the entirearea of the recording layer 172, fluorescence 175 a having a wavelengthλ3 a is produced from the site on the recording layer 172, at which sitethe material A has changed into the fluorescent material A. Also,fluorescence 175 b having a wavelength λ3 b is produced from the site onthe recording layer 172, at which site the material B has changed intothe fluorescent material B. Further, fluorescence 175 c having awavelength λ3 c is produced from the site on the recording layer 172, atwhich site the material C has changed into the fluorescent material C.Therefore, the fluorescence 175 a, the fluorescence 175 b, and thefluorescence 175 c may be spatially resolved and detected throughwavelength discrimination by use of, for example, an area sensorcomprising three kinds of fine photo detecting devices, which havedifferent spectral sensitivity regions and which are arrayed intwo-dimensional directions. In this manner, the recording information iscapable of being reproduced from the recording medium 170.

In cases where the three-color excitation light beams respectivelyhaving wavelengths, which primarily fall within the wavelength regionsof λ2 a, λ2 b, and λ2 c, are irradiated to the recording layer 172independently and with different timings, the fluorescence 175 a, thefluorescence 175 b, and the fluorescence 175 c are capable of beingdiscriminated and detected by use of one kind of photodetector, which iscapable of detecting all of the fluorescence having the wavelengths λ3a, λ3 b, and λ3 c.

In the recording medium in accordance with the present invention, thematerials employed for forming the recording layer are not limited tothe materials, which are employed in the recording medium 122 describedabove, and the recording layer may be formed from a combination ofmultiple kinds of the materials described below.

By way of example, the compound represented by Formula (I-4), which isone of the compounds represented by Formula (I) shown above, may beemployed as the material constituting the recording layer. The materialhas the properties such that, when the recording light having thewavelength of 350 nm is irradiated to the material, the material iscapable of being caused to change into a fluorescent material and suchthat, when the excitation light having the wavelength of 350 nm is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce the fluorescence.

Also, as the material constituting the recording layer, it is possibleto employ a material comprising a combination of the compound B-6, whichis one of the compounds represented by Formula (II-1) shown above andacting as the chemical species [FL] capable of producing thefluorescence, and the compound A- 4, which is one of the compoundsrepresented by Formula (II-2) shown above and acting as the chemicalspecies [Q] capable of quenching the fluorescence. The material has theproperties such that, when the recording light having the wavelength of532 nm is irradiated to the material, the material is capable of beingcaused to change into the fluorescent material and such that, when theexcitation light having the wavelength of 532 nm is then irradiated tothe thus formed fluorescent material, the fluorescent material iscapable of being caused to produce the fluorescence.

Further, as the material constituting the recording layer, it ispossible to employ a material comprising a combination of the compoundA-11, which is one of the compounds represented by Formula (II-3) shownabove and acting as the chemical species [FL] capable of producing thefluorescence, and the compound B-40, which is one of the compoundsrepresented by Formula (II-4) shown above and acting as the chemicalspecies [Q] capable of quenching the fluorescence. The material has theproperties such that, when the recording light having the wavelength of680 nm is irradiated to the material, the material is capable of beingcaused to change into the fluorescent material and such that, when theexcitation light having the wavelength of 680 nm is then irradiated tothe thus formed fluorescent material, the fluorescent material iscapable of being caused to produce the fluorescence.

Furthermore, as the material constituting the recording layer, it ispossible to employ a material comprising a combination of the compoundB-74, which is one of the compounds represented by Formula (II-5) shownabove and acting as the chemical species [FL] capable of producing thefluorescence, and the compound B-5, which is one of the compoundsrepresented by Formula (II-4) shown above and acting as the chemicalspecies [Q] capable of quenching the fluorescence. The material has theproperties such that, when the recording light having the wavelength of680 nm is irradiated to the material, the material is capable of beingcaused to change into the fluorescent material and such that, when theexcitation light having the wavelength of 680 nm is then irradiated tothe thus formed fluorescent material, the fluorescent material iscapable of being caused to produce the fluorescence.

Also, as the material constituting the recording layer, it is possibleto employ a material comprising a combination of the compound B-136,which is one of the compounds represented by Formula (II-6) shown aboveand acting as the chemical species [FL] capable of producing thefluorescence, and the compound B-64, which is one of the compoundsrepresented by Formula (II-4) shown above and acting as the chemicalspecies [Q] capable of quenching the fluorescence. The material has theproperties such that, when the recording light having the wavelength of532 nm is irradiated to the material, the material is capable of beingcaused to change into the fluorescent material and such that, when theexcitation light having the wavelength of 532 nm is then irradiated tothe thus formed fluorescent material, the fluorescent material iscapable of being caused to produce the fluorescence.

As an example of a combination of multiple kinds of materials, it ispossible to employ a combination of (a) a material comprising thecompound represented by Formula (I-4), which is one of the compoundsrepresented by Formula (I) shown above, and (b) a material comprising acombination of the compound B-6, which is one of the compoundsrepresented by Formula (II-1) shown above and acting as the chemicalspecies [FL] capable of producing the fluorescence, and the compoundA-4, which is one of the compounds represented by Formula (II-2) shownabove and acting as the chemical species [Q] capable of quenching thefluorescence. As for the material comprising the compound represented byFormula (I-4), the wavelength λ1 of the recording light, with which thematerial is caused to change into the fluorescent material, is equal to350 nm, the wavelength λ2 of the excitation light for the formedfluorescent material is equal to 532 nm, and the wavelength λ3 of thefluorescence produced by the fluorescent material is equal to 620 nm. Asfor the material comprising the combination of the compound B-6, whichis one of the compounds represented by Formula (II-1) shown above, andthe compound A-4, which is one of the compounds represented by Formula(II-2) shown above, the wavelength λ1 of the recording light, with whichthe material is caused to change into the fluorescent material, is equalto 640 nm, the wavelength λ2 of the excitation light for the formedfluorescent material is equal to640 nm, and the wavelength λ3 of thefluorescence produced by the fluorescent material is equal to 700 nm.

As a different example of a combination of multiple kinds of materials,it is possible to employ a combination of (a) a material comprising thecompound represented by Formula (I-4), which is one of the compoundsrepresented by Formula (I) shown above, and (b) a material comprising acombination of the compound λ-2, which is one of the compoundsrepresented by Formula (II-3) shown above and acting as the chemicalspecies [FL) capable of producing the fluorescence, and the compoundB-40, which is one of the compounds represented by Formula (II-4) shownabove and acting as the chemical species [Q] capable of quenching thefluorescence. As for the material comprising the compound represented byFormula (I-4), the wavelength λ1 of the recording light, with which thematerial is caused to change into the fluorescent material, is equal to350 nm, the wavelength λ2 of the excitation light for the formedfluorescent material is equal to 532 nm, and the wavelength λ3 of thefluorescence produced by the fluorescent material is equal to 620 nm. Asfor the material comprising the combination of the compound A-2, whichis one of the compounds represented by Formula (II-3) shown above, andthe compound B-40, which is one of the compounds represented by Formula(II-4) shown above, the wavelength λ1 of the recording light, with whichthe material is caused to change into the fluorescent material, is equalto 488 nm, the wavelength λ2 of the excitation light for the formedfluorescent material is equal to532 nm, and the wavelength λ3 of thefluorescence produced by the fluorescent material is equal to 580 nm.

1-66. (canceled)
 67. A recording medium, comprising: i) a substrate, andii) a recording layer overlaid on the substrate, wherein the recordinglayer comprises multiple kinds of materials uniformly mixed together,each of which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material, themultiple kinds of the materials are capable of being caused by therecording light having different wavelengths λ1 to change intofluorescent materials, the fluorescent materials, which have been formedby the multiple kinds of the materials, are capable of being caused byexcitation light having different wavelengths λ2 to producefluorescence, and the fluorescent materials, which have been formed bythe multiple kinds of the materials, produce the fluorescence havingdifferent wavelengths λ3.
 68. A recording medium, comprising: i) asubstrate, and ii) a recording layer overlaid on the substrate, whereinthe recording layer comprises multiple kinds of materials uniformlymixed together, each of which has properties such that, when recordinglight having a predetermined wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into afluorescent material, the multiple kinds of the materials are capable ofbeing caused by the recording light having different wavelengths λ1 tochange into fluorescent materials, the fluorescent materials, which havebeen formed by the multiple kinds of the materials, are capable of beingcaused by excitation light having an identical wavelength λ2 to producefluorescence, and the fluorescent materials, which have been formed bythe multiple kinds of the materials, produce the fluorescence havingdifferent wavelengths λ3.
 69. A recording medium, comprising: i) asubstrate, and ii) a recording layer overlaid on the substrate, whereinthe recording layer comprises multiple kinds of materials uniformlymixed together, each of which has properties such that, when recordinglight having a predetermined wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into afluorescent material, the multiple kinds of the materials are capable ofbeing caused by the recording light having different wavelengths λ1 tochange into fluorescent materials, the fluorescent materials, which havebeen formed by the multiple kinds of the materials, are capable of beingcaused by excitation light having different wavelengths λ2 to producefluorescence, and the fluorescent materials, which have been formed bythe multiple kinds of the materials, produce the fluorescence having anidentical wavelength λ3.
 70. A recording medium as defined in claim 67,68, or 69 wherein the recording layer is constituted of a thin film,which contains the multiple kinds of the materials mixed together.
 71. Arecording medium as defined in claim 67, 68, or 69 wherein the substratecomprises a dielectric material, a metal film is overlaid on one surfaceof the dielectric material, and the recording layer is overlaid on themetal film.
 72. A recording medium as defined in claim 71 wherein themetal film comprises a metal selected from the group consisting of goldand silver.
 73. A recording medium as defined in claim 67, 68, or 69wherein the substrate comprises a material permeable to the excitationlight having the wavelengths λ2.
 74. A recording medium as defined inclaim 67, 68, or 69 wherein at least one material among the multiplekinds of the materials, each of which has the properties such that, whenthe recording light having the predetermined wavelength λ1 is irradiatedto the material, the material is capable of being caused to change intothe fluorescent material, is a compound, in which a certain functionalgroup of a compound [FL] has been protected with a protecting group[PR]-, and in which the production of the fluorescence is therebyrestricted, the compound being represented by Formula (I):[FL]−[PR]  (I) wherein [FL] represents the compound residue capable ofproducing the fluorescence, and [PR] represents the group capable ofbeing separated from [FL] when light is irradiated to [FL].
 75. Arecording medium as defined in claim 67, 68, or 69 wherein at least onematerial among the multiple kinds of the materials, each of which hasthe properties such that, when the recording light having thepredetermined wavelength λ1 is irradiated to,the material, the materialis capable of being caused to change into the fluorescent material, is amaterial, which comprises a combination of a chemical species [FL]capable of producing the fluorescence and a chemical species [Q] capableof quenching the fluorescence, the material being represented by Formula(II):[FL]+[Q]  (II) wherein [FL] represents the chemical species capable ofproducing the fluorescence, and [Q] represents the chemical speciescapable of quenching the fluorescence.
 76. A recording medium as definedin claim 75 wherein the chemical species [FL] is a compound representedby Formula (II-1):

wherein Z¹ and Z² each represent an atom group necessary for forming afive-membered or six-membered, nitrogen-containing heterocyclic ring;R³⁰ and R³¹ each independently represent an alkyl group or an arylgroup; L³, L⁴, L⁵, L⁶, and L⁷ each independently represent a substitutedor unsubstituted methine group, provided that, in cases where L³ to L⁷are substituted by substituents, the substituents may optionally beconnected with one another to form a ring; p and q each independentlyrepresent 0 or 1; n1 and n2 each independently represent 0, 1, or 2; M1represents a charge balancing counter ion; and m1 represents a numbernecessary for keeping charge balance; and the chemical species [Q] is acompound represented by Formula (II-2):

wherein m and n each independently represent an integer of 0 to 2; X¹and X² each represent ═NR¹ or ═CR²R³, in which R¹, R², and R³ eachrepresent a substituent; and L¹ and L² each independently represent abivalent linking group.
 77. A recording medium as defined in claim 75wherein the chemical species [FL] is an anion represented by Formula(II-3):

wherein Za and Zb each independently represent an atom group necessaryfor forming a five-membered or six-membered, nitrogen-containingheterocyclic ring; R¹ and R² each independently represent an alkyl groupor an aryl group; L¹, L², L³, L⁴, and L⁵ each independently represent asubstituted or unsubstituted methine group, provided that, in caseswhere L¹ to L⁵ are substituted by substituents, the substituents mayoptionally be connected with one another to form a ring; n represents aninteger of at least 1; j represents 0, 1, or 2; and k represents 0 or 1;and the chemical species [Q] is a cation represented by Formula (11-4):

wherein R₅ and R₆ each independently represent a substituent group; R₇and R₈ each independently represent an alkyl group, an alkenyl group, analkynyl group, an aralkyl group, an aryl group or a heterocyclic group,provided that R₅ and R₆, R₅ and R₇, R₆ and R₈, or R₇ and R₈ may beconnected with each other to form a ring; and r and s each independentlyrepresent an integer of 0 to 4, provided that, in cases where r and seach represent an integer of at least 2, the at least two substituentsR₅ may be identical or different, and the at least two substituents R₆may be identical or different.
 78. A recording medium as defined inclaim 75 wherein the chemical species [FL] is an anion represented byeither one of Formula (II-5) and Formula (11-6):

wherein A¹, A², B¹, and B²each independently represent a substituent;L¹, L², L³, L⁴, and L⁵ each represent a methine group; X¹ represents ═),═NR, or ═C(CN)₂, in which R represents a substituent; X² represents —O,—NR, or —C(CN)₂, in which R represents a substituent; m and n eachrepresent an integer of 0 to 2; Y¹ and E each represent an atom or anatom group necessary for forming a carbocyclic ring or a heterocyclicring; Z¹ and G each represent an atom or an atom group necessary forforming a carbocyclic ring or a heterocyclic ring; x and y eachindependently represent 0 or 1; M^(k+) represents an onium ion; and krepresents the number of charges; and the chemical species [Q] is acation represented by Formula (11-4):

wherein R₅ and R₆ each independently represent a substituent group; R₇and R₈ each independently represent an alkyl group, an alkenyl group, analkynyl group, an aralkyl group, an aryl group or a heterocyclic group,provided that R₅ and R₆, R₅ and R₇, R₆ and R₈, or R₇ and R₈ may beconnected with each other to form a ring; and r and s each independentlyrepresent an integer of 0 to 4, provided that, in cases where r and seach represent an integer of at least 2, the at least two substituentsR₅ may be identical or different, and the at least two substituents R₆may be identical or different.
 79. An information recording method, inwhich information is recorded on a recording medium as defined in claim67, 68, or 69, the method comprising the step of: irradiating beams ofthe recording light carrying recording information and having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials.
 80. An information recording method as defined in claim 79wherein an evanescent wave, which has been radiated out from a range ofa diameter shorter than the wavelengths of the recording light, isemployed as the recording light.
 81. An information recording apparatus,in which information is recorded on a recording medium as defined inclaim 67, 68, or 69, the apparatus comprising: recording means forirradiating beams of the recording light carrying recording informationand having a plurality of different wavelengths, each of whichwavelengths is capable of causing one of the multiple kinds of thematerials to change into the fluorescent material, to the recordinglayer of the recording medium, such that the beams of the recordinglight are capable of impinging upon an identical site on the recordinglayer, in order to cause the multiple kinds of the materials, which arelocated it at the site having been exposed to the recording light, tochange into the fluorescent materials.
 82. An information recordingapparatus as defined in claim 81 wherein the recording means is providedwith a micro-aperture probe, which is provided with a light passageaperture having a diameter shorter than the wavelengths of the recordinglight, the light passage aperture being formed at one end of themicro-aperture probe, and the recording means irradiates an evanescentwave, which has been radiated out from the light passage aperture of themicro-aperture probe, to the recording layer.
 83. An informationrecording apparatus as defined in claim 81 wherein the recording meansirradiates an evanescent wave, which has been radiated out from a solidimmersion lens, to the recording layer.
 84. An information reproducingmethod for reproducing recording information from a recording medium asdefined in claim 67, on which the recording information has beenrecorded, wherein the recording information has been recorded on therecording medium by irradiating beams of the recording light carryingrecording information and having a plurality of different wavelengths,each of which wavelengths is capable of causing one of the multiplekinds of the materials to change into the fluorescent material, to therecording layer of the recording medium, such that the beams of therecording light are capable of impinging upon an identical site on therecording layer, the multiple kinds of the materials, which are locatedat the site having been exposed to the recording light, being therebycaused to change into the fluorescent materials, the method comprisingthe steps of: i) irradiating the excitation light having a plurality ofdifferent wavelengths, each of which wavelengths falls within anexcitation wavelength region for one of the fluorescent materials, tothe recording layer, the fluorescent materials being thereby caused toproduce the fluorescence having different wavelengths, and ii) detectingthe fluorescence through wavelength discrimination.
 85. An informationreproducing method for reproducing recording information from arecording medium as defined in claim 68, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating beams of therecording light carrying recording information and having a plurality ofdifferent wavelengths, each of which wavelengths is capable of causingone of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the method comprising the steps of: i) irradiating one kindof the excitation light having a wavelength, which falls within anexcitation wavelength region common to the fluorescent materials, to therecording layer, the fluorescent materials being thereby caused toproduce the fluorescence having different wavelengths, and ii) detectingthe fluorescence through wavelength discrimination.
 86. An informationreproducing method for reproducing recording information from arecording medium as defined in claim 69, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating beams of therecording light carrying recording information and having a plurality ofdifferent wavelengths, each of which wavelengths is capable of causingone of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the method comprising the steps of: i) irradiating theexcitation light having a plurality of different wavelengths, each ofwhich wavelengths falls within an excitation wavelength region for oneof the fluorescent materials, with different timings to the recordinglayer, the fluorescent materials being thereby caused to produce thefluorescence having the identical wavelength, and ii) detecting thefluorescence.
 87. An information reproducing method as defined in claim84, 85, or 86 wherein light having the wavelengths identical with thewavelengths of the recording light is employed as the excitation light,an intensity of the excitation light having the wavelengths is set at anintensity lower than the intensity of the recording light, and theexcitation light having the thus set intensity is irradiated to therecording layer.
 88. An information reproducing method as defined inclaim 84, 85, or 86 wherein light having the wavelengths different fromthe wavelengths of the recording light is employed as the excitationlight.
 89. An information reproducing method as defined in claim 84, 85,or 86 wherein light irradiated to a fine range is employed as theexcitation light, the recording layer is scanned with the excitationlight, and the fluorescence produced from the recording layer during thescanning with the excitation light is detected with respect to each ofpositions which are being scanned.
 90. An information reproducing methodas defined in claim 89 wherein an evanescent wave, which has beenradiated out from a range of a diameter shorter than the wavelength ofthe excitation light, is employed as the excitation light.
 91. Aninformation reproducing method as defined in claim 84, 85, or 86 whereinthe excitation light is entered into the substrate so as to propagatethrough repeated total reflection between two surfaces of the substrate,an evanescent wave, which oozes out from the substrate toward therecording layer when the excitation light is thus entered into thesubstrate, is irradiated to the recording layer, and the fluorescence,which has been produced from the recording layer when the evanescentwave is thus irradiated to the recording layer, is spatially resolvedand detected.
 92. An information reproducing method as defined in claim84, 85, or 86 wherein the recording medium is constituted such that thesubstrate comprises a dielectric material, a metal film is overlaid onone surface of the dielectric material, and the recording layer isoverlaid on the metal film, and the excitation light is irradiated fromthe substrate side to the recording medium such that the excitationlight impinges at a specific angle of incidence upon the metal film. 93.An information reproducing apparatus for reproducing recordinginformation from a recording medium as defined in claim 67, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiatingbeams of the recording light carrying recording information and having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the apparatus comprising: i) excitation means for irradiatingthe excitation light having a plurality of different wavelengths, eachof which wavelengths falls within an excitation wavelength region forone of the fluorescent materials, to the recording layer in order tocause the fluorescent materials to produce the fluorescence havingdifferent wavelengths, and ii) read-out means for detecting thefluorescence through wavelength discrimination.
 94. An informationreproducing apparatus for reproducing recording information from arecording medium as defined in claim 68, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating beams of therecording light carrying recording information and having a plurality ofdifferent wavelengths, each of which wavelengths is capable of causingone of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the apparatus comprising: i) excitation means for irradiatingone kind of the excitation light having a wavelength, which falls withinan excitation wavelength region common to the fluorescent materials, tothe recording layer in order to cause the fluorescent materials toproduce the fluorescence having different wavelengths, and ii) read-outmeans for detecting the fluorescence through wavelength discrimination.95. An information reproducing apparatus for reproducing recordinginformation from a recording medium as defined in claim 69, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiatingbeams of the recording light carrying recording information and having aplurality of different wavelengths, each of which wavelengths is capableof causing one of the multiple kinds of the materials to change into thefluorescent material, to the recording layer of the recording medium,such that the beams of the recording light are capable of impinging uponan identical site on the recording layer, the multiple kinds of thematerials, which are located at the site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterials, the apparatus comprising: i) excitation means for irradiatingthe excitation light having a plurality of different wavelengths, eachof which wavelengths falls within an excitation wavelength region forone of the fluorescent materials, with different timings to therecording layer in order to cause the fluorescent materials to producethe fluorescence having the identical wavelength, and ii) read-out meansfor detecting the fluorescence.
 96. An information reproducing apparatusas defined in claim 93, 94, or 95 wherein the excitation means scans therecording layer with converged beam-like excitation light, and theread-out means detects the fluorescence with respect to each ofpositions which are being scanned with the excitation light.
 97. Aninformation reproducing apparatus as defined in claim 96 wherein therecording medium is constituted such that the substrate comprises adielectric material, a metal film is overlaid on one surface of thedielectric material, and the recording layer is overlaid on the metalfilm, and the excitation means irradiates the excitation light to therecording medium such that the excitation light impinges upon the metalfilm from the substrate side.
 98. An information reproducing apparatusas defined in claim 93, 94, or 95 wherein the excitation means scans therecording layer with an evanescent wave, which has been radiated outfrom a solid immersion lens, and the read-out means detects thefluorescence with respect to each of positions which are being scannedwith the evanescent wave.
 99. An information reproducing apparatus asdefined in claim 93, 94, or 95 wherein the excitation means is providedwith a micro-aperture probe, which is provided with a light passageaperture having a diameter shorter than the wavelengths of theexcitation light, the light passage aperture being formed at one end ofthe micro-aperture probe, the excitation means scans the recording layerwith an evanescent wave, which has been radiated out from the lightpassage aperture of the micro-aperture probe, and the read-out meansdetects the fluorescence with respect to each of positions which arebeing scanned with the evanescent wave.
 100. An information reproducingapparatus as defined in claim 93, 94, or 95 wherein the excitation meansirradiates the excitation light into the substrate such that theexcitation light propagates through repeated total reflection betweentwo surfaces of the substrate, and such that an evanescent wave, whichoozes out from the substrate toward the recording layer when theexcitation light is thus entered into the substrate, is irradiated tothe recording layer, and the read-out means spatially resolves anddetects the fluorescence, which has been produced from the recordinglayer when the evanescent wave is thus irradiated to the recordinglayer.
 101. An information reproducing method for reproducing recordinginformation from a recording medium, on which the recording informationhas been recorded, wherein the recording information has been recordedon the recording medium by irradiating the recording light having thepredetermined wavelength λ1, which recording light carries the recordinginformation, to the recording layer of the recording medium, thematerial, which is located at a site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterial, the method comprising the steps of: i) providing the recordingmedium, the recording medium comprising: a substrate, and a recordinglayer overlaid on the substrate, wherein the recording layer comprises amaterial, which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence; ii)irradiating the excitation light having the wavelength λ2, which fallswithin an excitation wavelength region for the fluorescent material, tothe recording layer, the fluorescent material being thereby caused toproduce the fluorescence; and iii) detecting the fluorescence, whereinlight having the wavelength λ2 different from the wavelength λ1 of therecording light is employed as the excitation light.
 102. An informationreproducing method for reproducing recording information from arecording medium, on which the recording information has been recorded,wherein the recording information has been recorded on the recordingmedium by irradiating the recording light having the predeterminedwavelength λ1, which recording light carries the recording information,to the recording layer of the recording medium, the material, which islocated at a site having been exposed to the recording light, beingthereby caused to change into the fluorescent material, the methodcomprising the steps of: i) providing the recording medium, therecording medium comprising: a substrate, and a recording layer overlaidon the substrate, wherein the recording layer comprises a material,which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence; ii)irradiating the excitation light having the wavelength λ2, which fallswithin an excitation wavelength region for the fluorescent material, tothe recording layer, the fluorescent material being thereby caused toproduce the fluorescence; and iii) detecting the fluorescence, whereinthe excitation light is entered into the substrate so as to propagatethrough repeated total reflection between two surfaces of the substrate,wherein an evanescent wave, which oozes out from the substrate towardthe recording layer when the excitation light is thus entered into thesubstrate, is irradiated to the recording layer, and wherein thefluorescence, which has been produced from the recording layer when theevanescent wave is thus irradiated to the recording layer, is spatiallyresolved and detected.
 103. The information reproducing method of claim102, wherein the wavelength λ1 of the recording light and the wavelengthλ2 of the excitation light are identical with each other.
 104. Theinformation reproducing method of claim 102, wherein the wavelength λ1of the recording light and the wavelength λ2 of the excitation light aredifferent from each other.
 105. An information reproducing method forreproducing recording information from a recording medium, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight carries the recording information, to the recording layer of therecording medium, the material, which is located at a site having beenexposed to the recording light, being thereby caused to change into thefluorescent material, the method comprising the steps of: i) providingthe recording medium, the recording medium comprising: a substrate, anda recording layer overlaid on the substrate, wherein the recording layercomprises a material, which has properties such that, when recordinglight having a predetermined wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into afluorescent material and such that, when excitation light having awavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence; ii) irradiating the excitation light having the wavelengthλ2, which falls within an excitation wavelength region for thefluorescent material, to the recording layer, the fluorescent materialbeing thereby caused to produce the fluorescence; and iii) detecting thefluorescence, wherein the recording medium is constituted such that thesubstrate comprises a dielectric material, a metal film is overlaid onone surface of the dielectric material, and the recording layer isoverlaid on the metal film, and wherein the excitation light isirradiated from the substrate side to the recording medium such that theexcitation light impinges at a specific angle of incidence upon themetal film.
 106. The information reproducing method of claim 105,wherein the wavelength λ1 of the recording light and the wavelength λ2of the excitation light are identical with each other.
 107. Theinformation reproducing method of claim 105, wherein the wavelength λ1of the recording light and the wavelength λ2 of the excitation light aredifferent from each other.
 108. An information reproducing apparatus forreproducing recording information from a recording medium, on which therecording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight carries the recording information, to the recording layer of therecording medium, the material, which is located at a site having beenexposed to the recording light, being thereby caused to change into thefluorescent material, the apparatus comprising: i) excitation means forirradiating the excitation light having the wavelength λ2, which fallswithin an excitation wavelength region for the fluorescent material, tothe recording layer in order to cause the fluorescent material toproduce the fluorescence, and ii) read-out means for detecting thefluorescence, wherein the recording medium comprises: a substrate, and arecording layer overlaid on the substrate, wherein the recording layercomprises a material, which has properties such that, when recordinglight having a predetermined wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into afluorescent material and such that, when excitation light having awavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence, and wherein the excitation means irradiates light, whichhas the wavelength λ2 different from the wavelength λ1 of the recordinglight, as the excitation light to the recording layer.
 109. Aninformation reproducing apparatus for reproducing recording informationfrom a recording medium, on which the recording information has beenrecorded, wherein the recording information has been recorded on therecording medium by irradiating the recording light having thepredetermined wavelength λ1, which recording light carries the recordinginformation, to the recording layer of the recording medium, thematerial, which is located at a site having been exposed to therecording light, being thereby caused to change into the fluorescentmaterial, the apparatus comprising: i) excitation means for irradiatingthe excitation light having the wavelength λ2, which falls within anexcitation wavelength region for the fluorescent material, to therecording layer in order to cause the fluorescent material to producethe fluorescence, and ii) read-out means for detecting the fluorescence,wherein the recording medium comprises: a substrate, and a recordinglayer overlaid on the substrate, wherein the recording layer comprises amaterial, which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence, wherein theexcitation means scans the recording layer with converged beam-likeexcitation light, wherein the read-out means detects the fluorescencewith respect to each of positions which are being scanned with theexcitation light, wherein the recording medium is constituted such thatthe substrate comprises a dielectric material, a metal film is overlaidon one surface of the dielectric material, and the recording layer isoverlaid on the metal film, and wherein the excitation means irradiatesthe excitation light to the recording medium such that the excitationlight impinges upon the metal film from the substrate side.
 110. Theinformation reproducing apparatus of claim 109, wherein the wavelengthλ1 of the recording light and the wavelength λ2 of the excitation lightare identical with each other.
 111. The information reproducingapparatus of claim 109, wherein the wavelength λ1 of the recording lightand the wavelength λ2 of the excitation light are different from eachother.
 112. An information reproducing apparatus for reproducingrecording information from a recording medium, on which the recordinginformation has been recorded, wherein the recording information hasbeen recorded on the recording medium by irradiating the recording lighthaving the predetermined wavelength λ1, which recording light carriesthe recording information, to the recording layer of the recordingmedium, the material, which is located at a site having been exposed tothe recording light, being thereby caused to change into the fluorescentmaterial, the apparatus comprising: i) excitation means for irradiatingthe excitation light having the wavelength λ2, which falls within anexcitation wavelength region for the fluorescent material, to therecording layer in order to cause the fluorescent material to producethe fluorescence, and ii) read-out means for detecting the fluorescence,wherein the recording medium comprises: a substrate, and a recordinglayer overlaid on the substrate, wherein the recording layer comprises amaterial, which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence, wherein theexcitation means scans the recording layer with converged beam-likeexcitation light, wherein the read-out means detects the fluorescencewith respect to each of positions which are being scanned with theexcitation light, wherein the excitation means scans the recording layerwith an evanescent wave, which has been radiated out from a solidimmersion lens, and wherein the read-out means detects the fluorescencewith respect to each of positions which are being scanned with theevanescent wave.
 113. The information reproducing apparatus of claim112, wherein the wavelength λ1 of the recording light and the wavelengthλ2 of the excitation light are identical with each other.
 114. Theinformation reproducing apparatus of claim 112, wherein the wavelengthλ1 of the recording light and the wavelength λ2 of the excitation lightare different from each other.
 115. An information reproducing apparatusfor reproducing recording information from a recording medium, on whichthe recording information has been recorded, wherein the recordinginformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight carries the recording information, to the recording layer of therecording medium, the material, which is located at a site having beenexposed to the recording light, being thereby caused to change into thefluorescent material, the apparatus comprising: i) excitation means forirradiating the excitation light having the wavelength λ2, which fallswithin an excitation wavelength region for the fluorescent material, tothe recording layer in order to cause the fluorescent material toproduce the fluorescence, and ii) read-out means for detecting thefluorescence, wherein the recording medium comprises: a substrate, and arecording layer overlaid on the substrate, wherein the recording layercomprises a material, which has properties such that, when recordinglight having a predetermined wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into afluorescent material and such that, when excitation light having awavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence, wherein the excitation means irradiates the excitationlight into the substrate such that the excitation light propagatesthrough repeated total reflection between two surfaces of the substrate,and such that an evanescent wave, which oozes out from the substratetoward the recording layer when the excitation light is thus enteredinto the substrate, is irradiated to the recording layer, and whereinthe read-out means spatially resolves and detects the fluorescence,which has been produced from the recording layer when the evanescentwave is thus irradiated to the recording layer.
 116. The informationreproducing apparatus of claim 115, wherein the wavelength λ1 of therecording light and the wavelength λ2 of the excitation light areidentical with each other.
 117. The information reproducing apparatus ofclaim 115, wherein the wavelength λ1 of the recording light and thewavelength λ2 of the excitation light are different from each other.118. A recording medium, comprising: i) a substrate, and ii) a recordinglayer overlaid on the substrate, wherein the recording layer comprises amaterial, which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence having anintensity in accordance with the intensity of the recording light, andwherein the wavelength λ1 of the recording light and the wavelength λ2of the excitation light are different from each other.
 119. A recordingmedium, comprising: i) a substrate, and ii) a recording layer overlaidon the substrate, wherein the recording layer comprises a material,which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence having anintensity in accordance with the intensity of the recording light, andwherein the substrate comprises a dielectric material, a metal film isoverlaid on one surface of the dielectric material, and the recordinglayer is overlaid on the metal film.
 120. The recording medium of claim119, wherein the wavelength λ1 of the recording light and the wavelengthλ2 of the excitation light are identical with each other.
 121. Therecording medium of claim 119, wherein the wavelength λ1 of therecording light and the wavelength λ2 of the excitation light aredifferent from each other.
 122. The recording medium of claim 119,wherein the metal film comprises a metal selected from the groupconsisting of gold and silver.
 123. The recording medium of claim 120,wherein the metal film comprises a metal selected from the groupconsisting of gold and silver.
 124. The recording medium of claim 121,wherein the metal film comprises a metal selected from the groupconsisting of gold and silver.
 125. A recording medium, comprising: i) asubstrate, and ii) a recording layer overlaid on the substrate, whereinthe recording layer comprises a material, which has properties suchthat, when recording light having a predetermined wavelength λ1 isirradiated to the material, the material is capable of being caused tochange into a fluorescent material and such that, when excitation lighthaving a wavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence having an intensity in accordance with the intensity of therecording light, and wherein the substrate comprises a materialpermeable to the excitation light having the wavelength λ2.
 126. Therecording medium of claim 125, wherein the wavelength λ1 of therecording light and the wavelength λ2 of the excitation light areidentical with each other.
 127. The recording medium of claim 125,wherein the wavelength λ1 of the recording light and the wavelength λ2of the excitation light are different from each other.
 128. Amulti-valued information recording apparatus, in which multi-valuedinformation is recorded on a recording medium, the apparatus comprising:recording means for irradiating the recording light having thepredetermined wavelength λ1, which recording light has an intensity inaccordance with the multi-valued information, to the recording layer ofthe recording medium in order to cause the material, which is located ata site having been exposed to the recording light, to change into thefluorescent material, wherein the recording medium comprises: asubstrate, and a recording layer overlaid on the substrate, wherein therecording layer comprises a material, which has properties such that,when recording light having a predetermined wavelength λ1 is irradiatedto the material, the material is capable of being caused to change intoa fluorescent material and such that, when excitation light having awavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence having an intensity in accordance with the intensity of therecording light, and wherein the recording means irradiates anevanescent wave, which has been radiated out from a solid immersionlens, to the recording layer.
 129. The multi-valued informationrecording apparatus of claim 128, wherein the wavelength λ1 of therecording light and the wavelength λ2 of the excitation light areidentical with each other.
 130. The multi-valued information recordingapparatus of claim 128, wherein the wavelength λ1 of the recording lightand the wavelength λ2 of the excitation light are different from eachother.
 131. A multi-valued information reproducing method forreproducing multi-valued information from a recording medium, on whichthe multi-valued information has been recorded, wherein the multi-valuedinformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight has an intensity in accordance with the multi-valued information,to the recording layer of the recording medium, the material, which islocated at a site having been exposed to the recording light, beingthereby caused to change into the fluorescent material, the methodcomprising the steps of: i) providing the recording medium, therecording medium comprising: a substrate, and a recording layer overlaidon the substrate, wherein the recording layer comprises a material,which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence having anintensity in accordance with the intensity of the recording light; ii)irradiating the excitation light having the wavelength λ2, which fallswithin an excitation wavelength region for the fluorescent material, tothe recording layer, the fluorescent material being thereby caused toproduce the fluorescence having an intensity in accordance with theintensity of the recording light; and iii) detecting the fluorescence,wherein light having the wavelength λ2 different from the wavelength λ1of the recording light is employed as the excitation light.
 132. Amulti-valued information reproducing method for reproducing multi-valuedinformation from a recording medium, on which the multi-valuedinformation has been recorded, wherein the multi-valued information hasbeen recorded on the recording medium by irradiating the recording lighthaving the predetermined wavelength λ1, which recording light has anintensity in accordance with the multi-valued information, to therecording layer of the recording medium, the material, which is locatedat a site having been exposed to the recording light, being therebycaused to change into the fluorescent material, the method comprisingthe steps of: i) providing the recording medium, the recording mediumcomprising: a substrate, and a recording layer overlaid on thesubstrate, wherein the recording layer comprises a material, which hasproperties such that, when recording light having a predeterminedwavelength λ1 is irradiated to the material, the material is capable ofbeing caused to change into a fluorescent material and such that, whenexcitation light having a wavelength λ2 is then irradiated to the thusformed fluorescent material, the fluorescent material is capable ofbeing caused to produce fluorescence having an intensity in accordancewith the intensity of the recording light; ii) irradiating theexcitation light having the wavelength λ2, which falls within anexcitation wavelength region for the fluorescent material, to therecording layer, the fluorescent material being thereby caused toproduce the fluorescence having an intensity in accordance with theintensity of the recording light; and iii) detecting the fluorescence,wherein the excitation light is entered into the substrate so as topropagate through repeated total reflection between two surfaces of thesubstrate, wherein an evanescent wave, which oozes out from thesubstrate toward the recording layer when the excitation light is thusentered into the substrate, is irradiated to the recording layer, andwherein the fluorescence, which has been produced from the recordinglayer when the evanescent wave is thus irradiated to the recordinglayer, is spatially resolved and detected.
 133. The multi-valuedinformation reproducing method of claim 132, wherein the wavelength λ1of the recording light and the wavelength λ2 of the excitation light areidentical with each other.
 134. The multi-valued information reproducingmethod of claim 132, wherein the wavelength λ1 of the recording lightand the wavelength λ2 of the excitation light are different from eachother.
 135. A multi-valued information reproducing method forreproducing multi-valued information from a recording medium, on whichthe multi-valued information has been recorded, wherein the multi-valuedinformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight has an intensity in accordance with the multi-valued information,to the recording layer of the recording medium, the material, which islocated at a site having been exposed to the recording light, beingthereby caused to change into the fluorescent material, the methodcomprising the steps of: i) providing the recording medium, therecording medium comprising: a substrate, and a recording layer overlaidon the substrate, wherein the recording layer comprises a material,which has properties such that, when recording light having apredetermined wavelength λ1 is irradiated to the material, the materialis capable of being caused to change into a fluorescent material andsuch that, when excitation light having a wavelength λ2 is thenirradiated to the thus formed fluorescent material, the fluorescentmaterial is capable of being caused to produce fluorescence having anintensity in accordance with the intensity of the recording light; ii)irradiating the excitation light having the wavelength λ2, which fallswithin an excitation wavelength region for the fluorescent material, tothe recording layer, the fluorescent material being thereby caused toproduce the fluorescence having an intensity in accordance with theintensity of the recording light; and iii) detecting the fluorescence,wherein the recording medium is constituted such that the substratecomprises a dielectric material, a metal film is overlaid on one surfaceof the dielectric material, and the recording layer is overlaid on themetal film, and wherein the excitation light is irradiated from thesubstrate side to the recording medium such that the excitation lightimpinges at a specific angle of incidence upon the metal film.
 136. Themulti-valued information reproducing method of claim 135, wherein thewavelength λ1 of the recording light and the wavelength λ2 of theexcitation light are identical with each other.
 137. The multi-valuedinformation reproducing method of claim 135, wherein the wavelength λ1of the recording light and the wavelength λ2 of the excitation light aredifferent from each other.
 138. A multi-valued information reproducingapparatus for reproducing multi-valued information from a recordingmedium, on which the multi-valued information has been recorded, whereinthe multi-valued information has been recorded on the recording mediumby irradiating the recording light having the predetermined wavelengthλ1, which recording light has an intensity in accordance with themulti-valued information, to the recording layer of the recordingmedium, the material, which is located at a site having been exposed tothe recording light, being thereby caused to change into the fluorescentmaterial, the apparatus comprising: i) excitation means for irradiatingthe excitation light having the wavelength λ2, which falls within anexcitation wavelength region for the fluorescent material, to therecording layer in order to cause the fluorescent material to producethe fluorescence having an intensity in accordance with the intensity ofthe recording light; and ii) read-out means for detecting thefluorescence, wherein the recording medium comprises: a substrate, and arecording layer overlaid on the substrate, wherein the recording layercomprises a material, which has properties such that, when recordinglight having a predetermined wavelength λ1 is irradiated to thematerial, the material is capable of being caused to change into afluorescent material and such that, when excitation light having awavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence having an intensity in accordance with the intensity of therecording light, and wherein the excitation means irradiates light,which has the wavelength λ2 different from the wavelength λ1 of therecording light, as the excitation light to the recording layer.
 139. Amulti-valued information reproducing apparatus for reproducingmulti-valued information from a recording medium, on which themulti-valued information has been recorded, wherein the multi-valuedinformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight has an intensity in accordance with the multi-valued information,to the recording layer of the recording medium, the material, which islocated at a site having been exposed to the recording light, beingthereby caused to change into the fluorescent material, the apparatuscomprising: i) excitation means for irradiating the excitation lighthaving the wavelength λ2, which falls within an excitation wavelengthregion for the fluorescent material, to the recording layer in order tocause the fluorescent material to produce the fluorescence having anintensity in accordance with the intensity of the recording light; andii) read-out means for detecting the fluorescence, wherein the recordingmedium comprises: a substrate, and a recording layer overlaid on thesubstrate, wherein the recording layer comprises a material, which hasproperties such that, when recording light having a predeterminedwavelength λ1 is irradiated to the material, the material is capable ofbeing caused to change into a fluorescent material and such that, whenexcitation light having a wavelength λ2 is then irradiated to the thusformed fluorescent material, the fluorescent material is capable ofbeing caused to produce fluorescence having an intensity in accordancewith the intensity of the recording light, wherein the excitation meansscans the recording layer with converged beam-like excitation light,wherein the read-out means detects the fluorescence with respect to eachof positions which are being scanned with the excitation light, whereinthe recording medium is constituted such that the substrate comprises adielectric material, a metal film is overlaid on one surface of thedielectric material, and the recording layer is overlaid on the metalfilm, and wherein the excitation means irradiates the excitation lightto the recording medium such that the excitation light impinges upon themetal film from the substrate side.
 140. The multi-valued informationreproducing apparatus of claim 139, wherein the wavelength λ1 of therecording light and the wavelength λ2 of the excitation light areidentical with each other.
 141. The multi-valued information reproducingapparatus of claim 139, wherein the wavelength λ1 of the recording lightand the wavelength λ2 of the excitation light are different from eachother.
 142. A multi-valued information reproducing apparatus forreproducing multi-valued information from a recording medium, on whichthe multi-valued information has been recorded, wherein the multi-valuedinformation has been recorded on the recording medium by irradiating therecording light having the predetermined wavelength λ1, which recordinglight has an intensity in accordance with the multi-valued information,to the recording layer of the recording medium, the material, which islocated at a site having been exposed to the recording light, beingthereby caused to change into the fluorescent material, the apparatuscomprising: i) excitation means for irradiating the excitation lighthaving the wavelength λ2, which falls within an excitation wavelengthregion for the fluorescent material, to the recording layer in order tocause the fluorescent material to produce the fluorescence having anintensity in accordance with the intensity of the recording light; andii) read-out means for detecting the fluorescence, wherein the recordingmedium comprises: a substrate, and a recording layer overlaid on thesubstrate, wherein the recording layer comprises a material, which hasproperties such that, when recording light having a predeterminedwavelength λ1 is irradiated to the material, the material is capable ofbeing caused to change into a fluorescent material and such that, whenexcitation light having a wavelength λ2 is then irradiated to the thusformed fluorescent material, the fluorescent material is capable ofbeing caused to produce fluorescence having an intensity in accordancewith the intensity of the recording light, wherein the excitation meansscans the recording layer with converged beam-like excitation light,wherein the read-out means detects the fluorescence with respect to eachof positions which are being scanned with the excitation light, whereinthe excitation means scans the recording layer with an evanescent wave,which has been radiated out from a solid immersion lens, and wherein theread-out means detects the fluorescence with respect to each ofpositions which are being scanned with the evanescent wave.
 143. Themulti-valued information reproducing apparatus of claim 142, wherein thewavelength λ1 of the recording light and the wavelength λ2 of theexcitation light are identical with each other.
 144. The multi-valuedinformation reproducing apparatus of claim 142, wherein the wavelengthλ1 of the recording light and the wavelength λ2 of the excitation lightare different from each other.
 145. A multi-valued informationreproducing apparatus for reproducing multi-valued information from arecording medium, on which the multi-valued information has beenrecorded, wherein the multi-valued information has been recorded on therecording medium by irradiating the recording light having thepredetermined wavelength λ1, which recording light has an intensity inaccordance with the multi-valued information, to the recording layer ofthe recording medium, the material, which is located at a site havingbeen exposed to the recording light, being thereby caused to change intothe fluorescent material, the apparatus comprising: i) excitation meansfor irradiating the excitation light having the wavelength λ2, whichfalls within an excitation wavelength region for the fluorescentmaterial, to the recording layer in order to cause the fluorescentmaterial to produce the fluorescence having an intensity in accordancewith the intensity of the recording light; and ii) read-out means fordetecting the fluorescence, wherein the recording medium comprises: asubstrate, and a recording layer overlaid on the substrate, wherein therecording layer comprises a material, which has properties such that,when recording light having a predetermined wavelength λ1 is irradiatedto the material, the material is capable of being caused to change intoa fluorescent material and such that, when excitation light having awavelength λ2 is then irradiated to the thus formed fluorescentmaterial, the fluorescent material is capable of being caused to producefluorescence having an intensity in accordance with the intensity of therecording light, wherein the excitation means irradiates the excitationlight into the substrate such that the excitation light propagatesthrough repeated total reflection between two surfaces of the substrate,and such that an evanescent wave, which oozes out from the substratetoward the recording layer when the excitation light is thus enteredinto the substrate, is irradiated to the recording layer, and whereinthe read-out means spatially resolves and detects the fluorescence,which has been produced from the recording layer when the evanescentwave is thus irradiated to the recording layer.
 146. The multi-valuedinformation reproducing apparatus of claim 145, wherein the wavelengthλ1 of the recording light and the wavelength λ2 of the excitation lightare identical with each other.
 147. The multi-valued informationreproducing apparatus of claim 145, wherein the wavelength λ1 of therecording light and the wavelength λ2 of the excitation light aredifferent from each other.